{"product_id":"1-mod-21-teeth-spur-gears-45-steel-transmission-motor-gear-bore-6-6-35-8mm","title":"1 Mod 21 Teeth Spur Gears (45# Steel) Transmission Motor Gear Bore 6\/6.35\/8mm","description":"\u003cdiv class=\"hdiy-desc\"\u003e\n\n  \u003cdiv class=\"hdiy-overview\"\u003e\n    \u003ch2\u003e1 Mod 21 Teeth Spur Gears — Reliable Power Transmission for DIY Automation\u003c\/h2\u003e\n    \u003cp\u003eWhen your motor drive system demands precise torque transfer and consistent mesh engagement, a poorly matched gear becomes the weakest link in your build. Whether you are assembling a desktop CNC router, a robotic arm, or a custom conveyor mechanism, the 1 Mod 21 Teeth Spur Gear in 45# steel gives makers, engineers, and workshop builders a dependable transmission component that holds up under repeated load cycles.\u003c\/p\u003e\n    \u003cp\u003eEach gear is machined from 45# medium-carbon steel, offering a solid balance of hardness and machinability. The module is 1 (Mod 1), with 21 teeth and a standard 20° pressure angle. Bore options span 6 mm (~0.236 in), 6.35 mm (~0.250 in \/ 1\/4 in), and 8 mm (~0.315 in), covering the most common motor shaft diameters used in hobby and light-industrial automation.\u003c\/p\u003e\n    \u003cp\u003eTypical use cases include DIY robotics joint drives requiring a compact 1 mod spur gear set, CNC axis transmission systems pairing a stepper motor with a 21-tooth drive gear, and small conveyor or indexing table builds where a steel motor transmission gear ensures long service life without deformation under sustained torque.\u003c\/p\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-compat\"\u003e\n    \u003cspan class=\"hdiy-compat-icon\"\u003e⚙️\u003c\/span\u003e\n    Compatible with Mod 1 gear systems | 20° pressure angle | Pairs with 1 Mod pinions, racks, and mating gears of any tooth count\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-features\"\u003e\n    \u003ch2\u003e✅ Key Features of These 1 Mod 21 Teeth Spur Gears\u003c\/h2\u003e\n    \u003cul class=\"hdiy-list\"\u003e\n      \u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🔩\u003c\/span\u003e\u003cstrong\u003e45# Steel Construction\u003c\/strong\u003e — Medium-carbon steel provides solid hardness and wear resistance for sustained transmission duty in automation and robotics applications.\u003c\/li\u003e\n      \u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e📐\u003c\/span\u003e\u003cstrong\u003eMod 1 \/ 21 Teeth Specification\u003c\/strong\u003e — Standard module 1 tooth profile ensures accurate mesh with any compatible Mod 1 mating gear, rack, or pinion in your drivetrain.\u003c\/li\u003e\n      \u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🎯\u003c\/span\u003e\u003cstrong\u003eThree Bore Options\u003c\/strong\u003e — Available in 6 mm, 6.35 mm (1\/4 in), and 8 mm bore diameters to fit the most common stepper motor and DC motor shaft sizes without adapter sleeves.\u003c\/li\u003e\n      \u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e⚡\u003c\/span\u003e\u003cstrong\u003e20° Pressure Angle\u003c\/strong\u003e — Industry-standard pressure angle delivers smooth, low-noise tooth engagement and efficient torque transfer across the full contact ratio.\u003c\/li\u003e\n      \u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🔧\u003c\/span\u003e\u003cstrong\u003eSetscrew Hub Design\u003c\/strong\u003e — Machined hub with setscrew flat allows secure shaft locking and straightforward installation on keyed or plain motor shafts.\u003c\/li\u003e\n      \u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🏗️\u003c\/span\u003e\u003cstrong\u003eBroad Application Range\u003c\/strong\u003e — Suited for CNC routers, robotic joints, conveyor indexers, 3D printer extruder drives, and other light-to-medium duty DIY transmission builds.\u003c\/li\u003e\n    \u003c\/ul\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-table-wrap\"\u003e\n    \u003ch2\u003e📐 Technical Specifications — Spur Gear\u003c\/h2\u003e\n    \u003ctable\u003e\n      \u003ctbody\u003e\n        \u003ctr\u003e\n\u003cth\u003eModule (Mod)\u003c\/th\u003e\n\u003ctd\u003e1\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eNumber of Teeth\u003c\/th\u003e\n\u003ctd\u003e21\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003ePressure Angle\u003c\/th\u003e\n\u003ctd\u003e20°\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eMaterial\u003c\/th\u003e\n\u003ctd\u003e45# Medium-Carbon Steel\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eBore Diameter\u003c\/th\u003e\n\u003ctd\u003e6 mm \/ 6.35 mm \/ 8 mm (see variant options)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003ePitch Diameter\u003c\/th\u003e\n\u003ctd\u003e21 mm (0.827 in)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eOutside Diameter\u003c\/th\u003e\n\u003ctd\u003eApproximately 23 mm (0.906 in)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eFace Width\u003c\/th\u003e\n\u003ctd\u003eSee variant options\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eHub Style\u003c\/th\u003e\n\u003ctd\u003eSetscrew hub\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eFinish\u003c\/th\u003e\n\u003ctd\u003eNatural steel \/ lightly oiled\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eGear Type\u003c\/th\u003e\n\u003ctd\u003eExternal spur gear\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eApplication\u003c\/th\u003e\n\u003ctd\u003eMotor transmission, robotics, CNC, conveyor drives\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003c\/tbody\u003e\n    \u003c\/table\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-faq\"\u003e\n    \u003ch2\u003e❓ Frequently Asked Questions\u003c\/h2\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eHow do I choose the right bore size for my motor shaft?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eMeasure your motor shaft diameter with a caliper. Select 6 mm for most small stepper and DC motors, 6.35 mm (1\/4 in) for motors with imperial shafts common in North American hobby applications, and 8 mm for larger NEMA 23 steppers or brushless motors. The setscrew hub accommodates plain or flat-keyed shafts within each bore size.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eWill this gear mesh with my existing Mod 1 rack or pinion?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eYes. Any gear or rack with a Module 1 tooth profile and a matching 20° pressure angle will mesh correctly with this 21-tooth spur gear. Tooth count only affects gear ratio, not compatibility — you can pair it with any Mod 1 mating gear regardless of its tooth count.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eIs 45# steel strong enough for my CNC or robotics project?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003e45# steel (equivalent to AISI 1045) has a tensile strength of approximately 600–700 MPa in its normalized state, making it well-suited for light-to-medium duty transmission applications such as CNC routers, robotic joints, and conveyor indexers. For very high-torque or high-cycle industrial applications, consider a hardened or alloy steel gear instead.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eDoes this gear resist rust and corrosion?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003e45# steel is not inherently stainless. The gears are supplied with a light oil coating to prevent surface oxidation during storage and transit. For humid or outdoor environments, apply a thin layer of grease or anti-corrosion spray after installation. For corrosive environments, a stainless steel or plastic gear may be more appropriate.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eWhat gear ratio can I achieve with a 21-tooth spur gear?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eGear ratio is determined by the tooth count of the driver divided by the tooth count of the driven gear. For example, pairing this 21-tooth gear with a 42-tooth mating gear gives a 2:1 reduction ratio. Pairing it with a 7-tooth pinion gives a 1:3 speed increase. You can mix and match any Mod 1 gears to achieve your target ratio.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eCan I use this gear with a 3D printer extruder or Z-axis drive?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eYes. Mod 1 spur gears are commonly used in DIY 3D printer extruder gear sets and Z-axis lead screw drives. The 6 mm and 8 mm bore options cover the shaft sizes used by most NEMA 17 and NEMA 23 stepper motors. Verify your printer's existing gear module before ordering to ensure mesh compatibility.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eHow many gears are included per order?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eEach order includes one (1) spur gear in the bore size selected at checkout. If you need a matched gear pair or a complete gear set, simply add the required quantity to your cart or contact us for bulk pricing options.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-cta\"\u003e\n    🛒 Select your bore size above, then add to cart.\n  \u003c\/div\u003e\n\n\u003c\/div\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"FAQPage\",\n  \"mainEntity\": [\n    {\n      \"@type\": \"Question\",\n      \"name\": \"How do I choose the right bore size for my motor shaft?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Measure your motor shaft diameter with a caliper. Select 6 mm for most small stepper and DC motors, 6.35 mm (1\/4 in) for motors with imperial shafts common in North American hobby applications, and 8 mm for larger NEMA 23 steppers or brushless motors. The setscrew hub accommodates plain or flat-keyed shafts within each bore size.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Will this gear mesh with my existing Mod 1 rack or pinion?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Yes. Any gear or rack with a Module 1 tooth profile and a matching 20° pressure angle will mesh correctly with this 21-tooth spur gear. Tooth count only affects gear ratio, not compatibility.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Is 45# steel strong enough for my CNC or robotics project?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"45# steel has a tensile strength of approximately 600–700 MPa in its normalized state, making it well-suited for light-to-medium duty transmission applications such as CNC routers, robotic joints, and conveyor indexers.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Does this gear resist rust and corrosion?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"45# steel is not inherently stainless. The gears are supplied with a light oil coating. For humid or outdoor environments, apply a thin layer of grease or anti-corrosion spray after installation.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What gear ratio can I achieve with a 21-tooth spur gear?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Gear ratio is determined by the tooth count of the driver divided by the tooth count of the driven gear. For example, pairing this 21-tooth gear with a 42-tooth mating gear gives a 2:1 reduction ratio.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Can I use this gear with a 3D printer extruder or Z-axis drive?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Yes. Mod 1 spur gears are commonly used in DIY 3D printer extruder gear sets and Z-axis lead screw drives. The 6 mm and 8 mm bore options cover the shaft sizes used by most NEMA 17 and NEMA 23 stepper motors.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"How many gears are included per order?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Each order includes one (1) spur gear in the bore size selected at checkout.\"\n      }\n    }\n  ]\n}\n\u003c\/script\u003e","brand":"HomeDIYer","offers":[{"title":"1 Mod 21 Teeth \/ 6mm","offer_id":52443257176338,"sku":"LXDGLBZSJ057459x1","price":10.85,"currency_code":"USD","in_stock":true},{"title":"1 Mod 21 Teeth \/ 6.35mm","offer_id":52443257209106,"sku":"LXDGLCDPJ00518x1","price":11.74,"currency_code":"USD","in_stock":true},{"title":"1 Mod 21 Teeth \/ 8mm","offer_id":52443257241874,"sku":"LXDGLCDPJ00519x1","price":11.74,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0884\/8936\/1682\/files\/Main-04_4b7cebfe-c7ee-4d11-87ee-f7d38b018bdb.jpg?v=1784042769","url":"https:\/\/homediyer.com\/products\/1-mod-21-teeth-spur-gears-45-steel-transmission-motor-gear-bore-6-6-35-8mm","provider":"HomeDIYer","version":"1.0","type":"link"}