Transmission components: essential guide to gear nomenclature<\/title>\n\n <link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n <link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin=\"\">\n <link href=\"https:\/\/fonts.googleapis.com\/css2?family=Inter:wght@400;500;600;700&display=swap\" rel=\"stylesheet\">\n\n <style>\n *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }\n\n :root {\n --green: #1a6b3c;\n --green-dark: #0f4a28;\n --green-mid: #2d8a55;\n --green-light: #e8f4ed;\n --green-xlight: #f2faf5;\n --amber: #b45309;\n --amber-light: #fef3c7;\n\n --bg: #ffffff;\n --bg-soft: #f8f9fa;\n --bg-muted: #f1f3f5;\n --border: #e5e7eb;\n --border-mid: #d1d5db;\n\n --text-primary: #111827;\n --text-secondary: #4b5563;\n --text-muted: #9ca3af;\n\n --radius-sm: 6px;\n --radius-md: 8px;\n --radius-lg: 12px;\n --shadow-sm: 0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);\n --shadow-md: 0 4px 12px rgba(0,0,0,.08), 0 2px 4px rgba(0,0,0,.04);\n }\n\n body { min-height: 100vh; 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Obtained from the product of the module and the number of teeth.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n<div id=\"tt-evolvente\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Involute<\/div>\n <div class=\"glossary-tooltip__def\">Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n\n <div class=\"article-page\">\n <div class=\"article-body\">\n <div class=\"article-body__main\"><script type=\"application\/ld+json\">\n{\n \"@context\": \"https:\/\/schema.org\",\n \"@graph\": [\n {\n \"@type\": \"TechArticle\",\n \"@id\": \"#article\",\n \"headline\": \"Transmission components: essential guide to gear nomenclature\",\n \"description\": \"This guide gives you the basic terminology: what you need to read a datasheet, place a correct order, or understand why two gears can't be paired.\",\n \"inLanguage\": \"en\",\n \"mentions\": [\n {\n \"@id\": \"#term-diametro-primitivo\"\n },\n {\n \"@id\": \"#term-evolvente\"\n }\n ]\n },\n {\n \"@type\": \"DefinedTermSet\",\n \"@id\": \"#glossario\",\n \"name\": \"Glossario - Transmission components: essential guide to gear nomenclature\",\n \"hasDefinedTerm\": [\n {\n \"@type\": \"DefinedTerm\",\n \"@id\": \"#term-diametro-primitivo\",\n \"name\": \"Pitch diameter\",\n \"description\": \"Diameter of the theoretical circle at which contact occurs between two meshing gears. 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It ensures a constant transmission ratio even in the presence of small centre-distance errors.\",\n \"inDefinedTermSet\": \"#glossario\"\n }\n ]\n }\n ]\n}\n<\/script>\n\n\n\n <h1 class=\"article__title\">Transmission components: essential guide to gear nomenclature<\/h1>\n<p class=\"article__subtitle\">This guide gives you the basic terminology: what you need to read a datasheet, place a correct order, or understand why two gears can’t be paired.<\/p>\n<h2 class=\"article__h2\" id=\"what-a-gear-does\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"3\"><\/circle><path d=\"M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 0 1-2.83 2.83l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-4 0v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 0 1-2.83-2.83l.06-.06A1.65 1.65 0 0 0 4.68 15a1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1 0-4h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 0 1 2.83-2.83l.06.06A1.65 1.65 0 0 0 9 4.68a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 4 0v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 0 1 2.83 2.83l-.06.06A1.65 1.65 0 0 0 19.4 9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 0 4h-.09a1.65 1.65 0 0 0-1.51 1z\"><\/path><\/svg><\/span>\n What a gear does\n<\/h2>\n<p class=\"article__p\">A gear is a mechanism that transmits motion, torque and force from one component to another inside a machine. Two or more gears combined form a gear transmission, in which the transmitted forces vary as a function of the wheel radii.<\/p>\n<p class=\"article__p\">Conventional nomenclature distinguishes two basic elements of the pair: the smaller wheel is the <strong>pinion<\/strong>, the toothed wheel connected to the rotating source (the motor); the larger one is the <strong>gear wheel<\/strong>. The <strong>rack<\/strong>, by contrast, is a linear toothed element: a straight bar with teeth that, paired with the pinion, converts rotary motion into continuous linear movement.<\/p>\n<p class=\"article__p\">When the two wheels have different diameters, the system lets you vary the transmission ratio: you can increase torque by reducing angular speed, or do the opposite, increase speed at the expense of transmitted torque.<\/p>\n<h2 class=\"article__h2\" id=\"tooth-geometry\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"10\"><\/circle><line x1=\"22\" y1=\"12\" x2=\"18\" y2=\"12\"><\/line><line x1=\"6\" y1=\"12\" x2=\"2\" y2=\"12\"><\/line><line x1=\"12\" y1=\"6\" x2=\"12\" y2=\"2\"><\/line><line x1=\"12\" y1=\"22\" x2=\"12\" y2=\"18\"><\/line><\/svg><\/span>\n Tooth geometry\n<\/h2>\n<p class=\"article__p\">The teeth develop radially from the <strong>pitch surface<\/strong>, a cylindrical reference surface that divides the tooth into two zones. The part that projects outward is the <strong>tooth tip<\/strong>; the inner portion, close to the wheel center, is the <strong>tooth root<\/strong>. The lateral surfaces of the tooth form its <strong>profile<\/strong>.<\/p>\n<p class=\"article__p\">The profile divides into two parts relative to the pitch circle: the outer portion is called the <strong>face<\/strong>, the inner one the <strong>flank<\/strong>.<\/p>\n<p class=\"article__p\">The main geometric quantities of the tooth are:<\/p>\n<ul class=\"article__list\">\n <li> <strong>Addendum<\/strong>: radial distance between the <dfn id=\"def-diametro-primitivo\"><span class=\"glossary-term\" data-tooltip=\"tt-diametro-primitivo\" title=\"Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.\">pitch diameter<\/span><\/dfn> and the outside diameter of the gear.<\/li>\n <li><strong>Dedendum<\/strong>: radial distance between the pitch diameter and the root diameter.<\/li>\n <li><strong>Tooth height<\/strong>: sum of addendum and dedendum.<\/li>\n <li><strong>Tooth pitch<\/strong>: distance measured along the circumference between two corresponding points on consecutive teeth.<\/li>\n<\/ul>\n\n<figure class=\"article__figure\">\n <img decoding=\"async\" src=\"https:\/\/shop.stagnoligears.com\/wp-content\/uploads\/gear-nomenclature-1.webp\" alt=\"Gear nomenclature diagram\" \/>\n <figcaption>Gear nomenclature<\/figcaption>\n<\/figure>\n\n<h2 class=\"article__h2\" id=\"the-involute-profile\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"10\"><\/circle><\/svg><\/span>\n The involute profile\n<\/h2>\n<p class=\"article__p\">Among all existing tooth profiles, the most widespread in modern mechanical engineering is the <strong><dfn id=\"def-evolvente\"><span class=\"glossary-term\" data-tooltip=\"tt-evolvente\" title=\"Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.\">involute<\/span><\/dfn> profile<\/strong>. It is generated geometrically from a point on a straight line that unwinds while keeping tangent contact with a fixed circle throughout its motion.<\/p>\n<p class=\"article__p\">The involute profile is preferred for two practical reasons: it guarantees uniform, regular meshing, tolerating variations in center distance without compromising operation; its production is simpler thanks to the use of standardized tools.<\/p>\n<div class=\"infobox infobox--grey\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M14.7 6.3a1 1 0 0 0 0 1.4l1.6 1.6a1 1 0 0 0 1.4 0l3.77-3.77a6 6 0 0 1-7.94 7.94l-6.91 6.91a2.12 2.12 0 0 1-3-3l6.91-6.91a6 6 0 0 1 7.94-7.94l-3.76 3.76z\"><\/path><\/svg>\n Technical note\n <\/div>\n <p class=\"infobox__text\">For correct meshing, two gears must have the same pitch on their pitch surfaces. In design terms, this means the same value of the module, the parameter that normalizes tooth dimensions relative to the number of teeth. Different modules: meshing impossible.<\/p>\n<\/div>\n<h2 class=\"article__h2\" id=\"reference-quantities-for-design\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><rect x=\"2\" y=\"2\" width=\"20\" height=\"20\" rx=\"2\" ry=\"2\"><\/rect><line x1=\"8\" y1=\"6\" x2=\"16\" y2=\"6\"><\/line><line x1=\"8\" y1=\"10\" x2=\"14\" y2=\"10\"><\/line><line x1=\"8\" y1=\"14\" x2=\"16\" y2=\"14\"><\/line><line x1=\"8\" y1=\"18\" x2=\"12\" y2=\"18\"><\/line><\/svg><\/span>\n Reference quantities for design\n<\/h2>\n<p class=\"article__p\">Designing a gear transmission requires certain fundamental geometric quantities. The main ones are summarized here:<\/p>\n<div class=\"article__table-wrap\">\n<table class=\"article__table\">\n<thead><tr><th>Quantity<\/th><th>Symbol<\/th><th>Definition<\/th><th>Importance<\/th><\/tr><\/thead>\n<tbody><tr><td>Module<\/td><td>m<\/td><td>Ratio between pitch and \u03c0; parameter that defines tooth size and compatibility.<\/td><td>Ensures compatibility between different gears.<\/td><\/tr>\n<tr><td>Pitch<\/td><td>p<\/td><td>Distance between two consecutive corresponding teeth measured along the pitch circle.<\/td><td>Determines tooth spacing and affects meshing.<\/td><\/tr>\n<tr><td>Operating center distance<\/td><td>a<\/td><td>Distance between the centers of the pitch surfaces of the two paired wheels.<\/td><td>Critical for correct load distribution and pairing life.<\/td><\/tr>\n<tr><td>Chordal distance (Wildhaber)<\/td><td>W<\/td><td>Measurement of pitch and tooth thickness taken with a micrometer over a defined number of teeth.<\/td><td>Practical method to verify tolerance conformity without complex instruments.<\/td><\/tr><\/tbody>\n<\/table>\n<\/div>\n<p class=\"article__p\">The operating center distance is critical during assembly: a wrong value compromises force transmission and causes premature wear. The Wildhaber chordal distance, by contrast, is a simple inspection tool to check tooth accuracy and compliance with design tolerances.<\/p>\n<div class=\"warnbox\">\n <div class=\"warnbox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M10.29 3.86L1.82 18a2 2 0 0 0 1.71 3h16.94a2 2 0 0 0 1.71-3L13.71 3.86a2 2 0 0 0-3.42 0z\"><\/path><line x1=\"12\" y1=\"9\" x2=\"12\" y2=\"13\"><\/line><line x1=\"12\" y1=\"17\" x2=\"12.01\" y2=\"17\"><\/line><\/svg>\n Warning\n <\/div>\n <p class=\"warnbox__text\">The operating center distance is not a figure to estimate by eye. Even a small error during assembly translates into non-uniform load distribution and accelerated wear.<\/p>\n<\/div>\n<h2 class=\"article__h2\" id=\"in-the-next-guides\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M2 3h6a4 4 0 0 1 4 4v14a3 3 0 0 0-3-3H2z\"><\/path><path d=\"M22 3h-6a4 4 0 0 0-4 4v14a3 3 0 0 1 3-3h7z\"><\/path><\/svg><\/span>\n In the next guides\n<\/h2>\n<p class=\"article__p\">This guide covers basic nomenclature. In the following Technical Center guides you’ll find detailed coverage of the different gear types (spur, helical, bevel, worm) and the selection criteria based on the specific application.<\/p>\n<div class=\"infobox\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M4 4h16c1.1 0 2 .9 2 2v12c0 1.1-.9 2-2 2H4c-1.1 0-2-.9-2-2V6c0-1.1.9-2 2-2z\"><\/path><polyline points=\"22,6 12,13 2,6\"><\/polyline><\/svg>\n Ask us\n <\/div>\n <p class=\"infobox__text\">If you have doubts about terminology for a specific application or need support reading a datasheet, <a href=\"https:\/\/shop.stagnoligears.com\/en\/contacts\/\" target=\"_blank\" rel=\"noopener\" class=\"cta-link\">contact<\/a> the technical office.<\/p>\n<\/div>\n\n <\/div>\n <\/div>\n <\/div>\n\n\n<script>\n (function () {\n var 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})();\n<\/script>\n\n<\/body><\/html>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>This guide gives you the basic terminology: what you need to read a datasheet, place a correct order, or understand why two gears can’t be paired.<\/p>\n","protected":false},"parent":0,"template":"","meta":{"_acf_changed":false},"campo-applicazione":[5453],"categoria-ct":[5442],"class_list":["post-25460","centro-tecnico","type-centro-tecnico","status-publish","hentry","campo-applicazione-geometry","categoria-ct-gear-fundamentals"],"acf":[],"yoast_head":"\n<title>Transmission Components: Gear Nomenclature | Stagnoli Gears Shop<\/title>\n<meta name=\"description\" content=\"Essential guide to gear nomenclature: learn the meaning of pinion, gear wheel, rack, module, tooth profile and key transmission components.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" 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{"id":25460,"date":"2026-06-15T14:15:12","date_gmt":"2026-06-15T12:15:12","guid":{"rendered":"https:\/\/shop.stagnoligears.com\/centro-tecnico\/organi-di-trasmissione-guida-essenziale-alla-nomenclatura-degli-ingranaggi\/"},"modified":"2026-07-10T14:40:17","modified_gmt":"2026-07-10T12:40:17","slug":"transmission-components-essential-guide","status":"publish","type":"centro-tecnico","link":"https:\/\/shop.stagnoligears.com\/en\/technical-hub\/transmission-components-essential-guide\/","title":{"rendered":"Transmission components: essential guide to gear nomenclature"},"content":{"rendered":"\n\n \n \n \n Transmission components: essential guide to gear nomenclature<\/title>\n\n <link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n <link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin=\"\">\n <link href=\"https:\/\/fonts.googleapis.com\/css2?family=Inter:wght@400;500;600;700&display=swap\" rel=\"stylesheet\">\n\n <style>\n *, *::before, *::after { box-sizing: border-box; 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}\n\n .badge {\n display: inline-block;\n font-size: 12px;\n font-weight: 600;\n padding: 2px 8px;\n border-radius: 20px;\n background: var(--green-light);\n color: var(--green-dark);\n }\n\n \/* ============================================================\n RESPONSIVE\n ============================================================ *\/\n @media (max-width: 900px) {\n .article-body { flex-direction: column; padding: 20px 20px 48px; }\n }\n \n \/* Glossary tooltips *\/\n .glossary-term {\n border-bottom: 1px dotted var(--green);\n color: var(--green);\n font-style: italic;\n cursor: help;\n }\n .glossary-tooltip {\n position: fixed;\n z-index: 9999;\n background: #fff;\n border: 1px solid var(--border-mid);\n border-radius: var(--radius-md);\n box-shadow: var(--shadow-md);\n padding: 10px 14px;\n max-width: 300px;\n font-family: 'Inter', sans-serif;\n font-size: 13px;\n }\n .glossary-tooltip__title {\n font-weight: 600;\n color: var(--text-primary);\n margin-bottom: 4px;\n }\n .glossary-tooltip__def {\n font-size: 12.5px;\n color: var(--text-secondary);\n line-height: 1.6;\n }\n .glossary-tooltip__tag {\n display: inline-block;\n margin-top: 6px;\n font-size: 9px;\n font-weight: 600;\n padding: 2px 7px;\n border-radius: 20px;\n background: var(--green-light);\n color: var(--green-dark);\n text-transform: uppercase;\n letter-spacing: 0.04em;\n }\n\n <\/style>\n<\/head>\n<body>\n\n<div id=\"tt-diametro-primitivo\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Pitch diameter<\/div>\n <div class=\"glossary-tooltip__def\">Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n<div id=\"tt-evolvente\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Involute<\/div>\n <div class=\"glossary-tooltip__def\">Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n\n <div class=\"article-page\">\n <div class=\"article-body\">\n <div class=\"article-body__main\"><script type=\"application\/ld+json\">\n{\n \"@context\": \"https:\/\/schema.org\",\n \"@graph\": [\n {\n \"@type\": \"TechArticle\",\n \"@id\": \"#article\",\n \"headline\": \"Transmission components: essential guide to gear nomenclature\",\n \"description\": \"This guide gives you the basic terminology: what you need to read a datasheet, place a correct order, or understand why two gears can't be paired.\",\n \"inLanguage\": \"en\",\n \"mentions\": [\n {\n \"@id\": \"#term-diametro-primitivo\"\n },\n {\n \"@id\": \"#term-evolvente\"\n }\n ]\n },\n {\n \"@type\": \"DefinedTermSet\",\n \"@id\": \"#glossario\",\n \"name\": \"Glossario - Transmission components: essential guide to gear nomenclature\",\n \"hasDefinedTerm\": [\n {\n \"@type\": \"DefinedTerm\",\n \"@id\": \"#term-diametro-primitivo\",\n \"name\": \"Pitch diameter\",\n \"description\": \"Diameter of the theoretical circle at which contact occurs between two meshing gears. 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It ensures a constant transmission ratio even in the presence of small centre-distance errors.\",\n \"inDefinedTermSet\": \"#glossario\"\n }\n ]\n }\n ]\n}\n<\/script>\n\n\n\n <h1 class=\"article__title\">Transmission components: essential guide to gear nomenclature<\/h1>\n<p class=\"article__subtitle\">This guide gives you the basic terminology: what you need to read a datasheet, place a correct order, or understand why two gears can’t be paired.<\/p>\n<h2 class=\"article__h2\" id=\"what-a-gear-does\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"3\"><\/circle><path d=\"M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 0 1-2.83 2.83l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-4 0v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 0 1-2.83-2.83l.06-.06A1.65 1.65 0 0 0 4.68 15a1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1 0-4h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 0 1 2.83-2.83l.06.06A1.65 1.65 0 0 0 9 4.68a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 4 0v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 0 1 2.83 2.83l-.06.06A1.65 1.65 0 0 0 19.4 9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 0 4h-.09a1.65 1.65 0 0 0-1.51 1z\"><\/path><\/svg><\/span>\n What a gear does\n<\/h2>\n<p class=\"article__p\">A gear is a mechanism that transmits motion, torque and force from one component to another inside a machine. Two or more gears combined form a gear transmission, in which the transmitted forces vary as a function of the wheel radii.<\/p>\n<p class=\"article__p\">Conventional nomenclature distinguishes two basic elements of the pair: the smaller wheel is the <strong>pinion<\/strong>, the toothed wheel connected to the rotating source (the motor); the larger one is the <strong>gear wheel<\/strong>. The <strong>rack<\/strong>, by contrast, is a linear toothed element: a straight bar with teeth that, paired with the pinion, converts rotary motion into continuous linear movement.<\/p>\n<p class=\"article__p\">When the two wheels have different diameters, the system lets you vary the transmission ratio: you can increase torque by reducing angular speed, or do the opposite, increase speed at the expense of transmitted torque.<\/p>\n<h2 class=\"article__h2\" id=\"tooth-geometry\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"10\"><\/circle><line x1=\"22\" y1=\"12\" x2=\"18\" y2=\"12\"><\/line><line x1=\"6\" y1=\"12\" x2=\"2\" y2=\"12\"><\/line><line x1=\"12\" y1=\"6\" x2=\"12\" y2=\"2\"><\/line><line x1=\"12\" y1=\"22\" x2=\"12\" y2=\"18\"><\/line><\/svg><\/span>\n Tooth geometry\n<\/h2>\n<p class=\"article__p\">The teeth develop radially from the <strong>pitch surface<\/strong>, a cylindrical reference surface that divides the tooth into two zones. The part that projects outward is the <strong>tooth tip<\/strong>; the inner portion, close to the wheel center, is the <strong>tooth root<\/strong>. The lateral surfaces of the tooth form its <strong>profile<\/strong>.<\/p>\n<p class=\"article__p\">The profile divides into two parts relative to the pitch circle: the outer portion is called the <strong>face<\/strong>, the inner one the <strong>flank<\/strong>.<\/p>\n<p class=\"article__p\">The main geometric quantities of the tooth are:<\/p>\n<ul class=\"article__list\">\n <li> <strong>Addendum<\/strong>: radial distance between the <dfn id=\"def-diametro-primitivo\"><span class=\"glossary-term\" data-tooltip=\"tt-diametro-primitivo\" title=\"Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.\">pitch diameter<\/span><\/dfn> and the outside diameter of the gear.<\/li>\n <li><strong>Dedendum<\/strong>: radial distance between the pitch diameter and the root diameter.<\/li>\n <li><strong>Tooth height<\/strong>: sum of addendum and dedendum.<\/li>\n <li><strong>Tooth pitch<\/strong>: distance measured along the circumference between two corresponding points on consecutive teeth.<\/li>\n<\/ul>\n\n<figure class=\"article__figure\">\n <img decoding=\"async\" src=\"https:\/\/shop.stagnoligears.com\/wp-content\/uploads\/gear-nomenclature-1.webp\" alt=\"Gear nomenclature diagram\" \/>\n <figcaption>Gear nomenclature<\/figcaption>\n<\/figure>\n\n<h2 class=\"article__h2\" id=\"the-involute-profile\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"10\"><\/circle><\/svg><\/span>\n The involute profile\n<\/h2>\n<p class=\"article__p\">Among all existing tooth profiles, the most widespread in modern mechanical engineering is the <strong><dfn id=\"def-evolvente\"><span class=\"glossary-term\" data-tooltip=\"tt-evolvente\" title=\"Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.\">involute<\/span><\/dfn> profile<\/strong>. It is generated geometrically from a point on a straight line that unwinds while keeping tangent contact with a fixed circle throughout its motion.<\/p>\n<p class=\"article__p\">The involute profile is preferred for two practical reasons: it guarantees uniform, regular meshing, tolerating variations in center distance without compromising operation; its production is simpler thanks to the use of standardized tools.<\/p>\n<div class=\"infobox infobox--grey\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M14.7 6.3a1 1 0 0 0 0 1.4l1.6 1.6a1 1 0 0 0 1.4 0l3.77-3.77a6 6 0 0 1-7.94 7.94l-6.91 6.91a2.12 2.12 0 0 1-3-3l6.91-6.91a6 6 0 0 1 7.94-7.94l-3.76 3.76z\"><\/path><\/svg>\n Technical note\n <\/div>\n <p class=\"infobox__text\">For correct meshing, two gears must have the same pitch on their pitch surfaces. In design terms, this means the same value of the module, the parameter that normalizes tooth dimensions relative to the number of teeth. Different modules: meshing impossible.<\/p>\n<\/div>\n<h2 class=\"article__h2\" id=\"reference-quantities-for-design\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><rect x=\"2\" y=\"2\" width=\"20\" height=\"20\" rx=\"2\" ry=\"2\"><\/rect><line x1=\"8\" y1=\"6\" x2=\"16\" y2=\"6\"><\/line><line x1=\"8\" y1=\"10\" x2=\"14\" y2=\"10\"><\/line><line x1=\"8\" y1=\"14\" x2=\"16\" y2=\"14\"><\/line><line x1=\"8\" y1=\"18\" x2=\"12\" y2=\"18\"><\/line><\/svg><\/span>\n Reference quantities for design\n<\/h2>\n<p class=\"article__p\">Designing a gear transmission requires certain fundamental geometric quantities. The main ones are summarized here:<\/p>\n<div class=\"article__table-wrap\">\n<table class=\"article__table\">\n<thead><tr><th>Quantity<\/th><th>Symbol<\/th><th>Definition<\/th><th>Importance<\/th><\/tr><\/thead>\n<tbody><tr><td>Module<\/td><td>m<\/td><td>Ratio between pitch and \u03c0; parameter that defines tooth size and compatibility.<\/td><td>Ensures compatibility between different gears.<\/td><\/tr>\n<tr><td>Pitch<\/td><td>p<\/td><td>Distance between two consecutive corresponding teeth measured along the pitch circle.<\/td><td>Determines tooth spacing and affects meshing.<\/td><\/tr>\n<tr><td>Operating center distance<\/td><td>a<\/td><td>Distance between the centers of the pitch surfaces of the two paired wheels.<\/td><td>Critical for correct load distribution and pairing life.<\/td><\/tr>\n<tr><td>Chordal distance (Wildhaber)<\/td><td>W<\/td><td>Measurement of pitch and tooth thickness taken with a micrometer over a defined number of teeth.<\/td><td>Practical method to verify tolerance conformity without complex instruments.<\/td><\/tr><\/tbody>\n<\/table>\n<\/div>\n<p class=\"article__p\">The operating center distance is critical during assembly: a wrong value compromises force transmission and causes premature wear. The Wildhaber chordal distance, by contrast, is a simple inspection tool to check tooth accuracy and compliance with design tolerances.<\/p>\n<div class=\"warnbox\">\n <div class=\"warnbox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M10.29 3.86L1.82 18a2 2 0 0 0 1.71 3h16.94a2 2 0 0 0 1.71-3L13.71 3.86a2 2 0 0 0-3.42 0z\"><\/path><line x1=\"12\" y1=\"9\" x2=\"12\" y2=\"13\"><\/line><line x1=\"12\" y1=\"17\" x2=\"12.01\" y2=\"17\"><\/line><\/svg>\n Warning\n <\/div>\n <p class=\"warnbox__text\">The operating center distance is not a figure to estimate by eye. Even a small error during assembly translates into non-uniform load distribution and accelerated wear.<\/p>\n<\/div>\n<h2 class=\"article__h2\" id=\"in-the-next-guides\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M2 3h6a4 4 0 0 1 4 4v14a3 3 0 0 0-3-3H2z\"><\/path><path d=\"M22 3h-6a4 4 0 0 0-4 4v14a3 3 0 0 1 3-3h7z\"><\/path><\/svg><\/span>\n In the next guides\n<\/h2>\n<p class=\"article__p\">This guide covers basic nomenclature. In the following Technical Center guides you’ll find detailed coverage of the different gear types (spur, helical, bevel, worm) and the selection criteria based on the specific application.<\/p>\n<div class=\"infobox\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M4 4h16c1.1 0 2 .9 2 2v12c0 1.1-.9 2-2 2H4c-1.1 0-2-.9-2-2V6c0-1.1.9-2 2-2z\"><\/path><polyline points=\"22,6 12,13 2,6\"><\/polyline><\/svg>\n Ask us\n <\/div>\n <p class=\"infobox__text\">If you have doubts about terminology for a specific application or need support reading a datasheet, <a href=\"https:\/\/shop.stagnoligears.com\/en\/contacts\/\" target=\"_blank\" rel=\"noopener\" class=\"cta-link\">contact<\/a> the technical office.<\/p>\n<\/div>\n\n <\/div>\n <\/div>\n <\/div>\n\n\n<script>\n (function () {\n var 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})();\n<\/script>\n\n<\/body><\/html>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>This guide gives you the basic terminology: what you need to read a datasheet, place a correct order, or understand why two gears can’t be paired.<\/p>\n","protected":false},"parent":0,"template":"","meta":{"_acf_changed":false},"campo-applicazione":[5453],"categoria-ct":[5442],"class_list":["post-25460","centro-tecnico","type-centro-tecnico","status-publish","hentry","campo-applicazione-geometry","categoria-ct-gear-fundamentals"],"acf":[],"yoast_head":"\n<title>Transmission Components: Gear Nomenclature | Stagnoli Gears Shop<\/title>\n<meta name=\"description\" content=\"Essential guide to gear nomenclature: learn the meaning of pinion, gear wheel, rack, module, tooth profile and key transmission components.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" 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