{"product_id":"0-5-mod-pinion-gear-black-steel-spur-gears-with-step-transmission-gear-25-teeth","title":"0.5 Mod Pinion Gear Black Steel Spur Gears with Step Transmission Gear 25 Teeth","description":"\u003cdiv class=\"hdiy-desc\"\u003e\n\n\u003cdiv class=\"hdiy-overview\"\u003e\n\u003ch2\u003e0.5 Mod Pinion Spur Gear — Compact Black Steel Step Transmission Gear for Precision Drives\u003c\/h2\u003e\n\u003cp\u003eFinding a small-module spur gear that fits a specific bore diameter without custom machining is a recurring challenge for RC hobbyists, robotics builders, and small-machine designers. This 0.5 mod pinion gear in black steel delivers a ready-to-install 25-tooth spur gear with a stepped hub design, available in three bore diameters to match the most common motor shaft sizes used in compact drive systems.\u003c\/p\u003e\n\u003cp\u003eEach gear is machined from black steel — a carbon steel with a black oxide surface treatment that provides moderate corrosion resistance and a clean, low-reflectance finish. The module is 0.5, giving a pitch diameter of 12.5 mm (approx. 0.492 in) and an outer (tip) diameter of approximately 13.5 mm (approx. 0.531 in). The stepped hub extends the gear's axial engagement length beyond the face width, improving shaft grip and set-screw retention. Bore options are 4 mm, 5 mm, and 6 mm to suit common motor and shaft standards.\u003c\/p\u003e\n\u003cp\u003eTypical applications include RC car and truck drivetrain pinion gears where a 0.5-module mesh is required, stepper motor output gears in compact robotics and automation rigs, and small gearbox stages in DIY CNC pen plotters, camera sliders, and motorized mechanisms where a low-profile 25-tooth spur gear keeps the gear train tight and efficient.\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\u003cstrong\u003eCompatibility:\u003c\/strong\u003e Meshes with any 0.5-module (Mod 0.5 \/ M0.5) spur or rack gear. Select the bore diameter that matches your motor or drive shaft. Set-screw retention — ensure your shaft has a flat or use thread-locking compound for round shafts.\n\u003c\/div\u003e\n\n\u003cdiv class=\"hdiy-features\"\u003e\n\u003ch2\u003e✅ Key Features of These 0.5 Mod Pinion Spur Gears\u003c\/h2\u003e\n\u003cdiv class=\"hdiy-list\"\u003e\n\u003cdiv\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🔩\u003c\/span\u003e\u003cstrong\u003eStepped Hub Design for Secure Shaft Retention\u003c\/strong\u003e\u003cbr\u003eThe extended stepped hub increases the axial contact length between the gear bore and the shaft, giving the set screw more material to clamp against and reducing the risk of the gear walking axially under load — a common failure mode in thin-hub pinion gears.\u003c\/div\u003e\n\u003cdiv\u003e\n\u003cspan class=\"hdiy-icon\"\u003e⚫\u003c\/span\u003e\u003cstrong\u003eBlack Oxide Steel Construction\u003c\/strong\u003e\u003cbr\u003eMachined from carbon steel with a black oxide finish, these gears offer the tooth strength needed for moderate-load drive applications while the surface treatment reduces surface rust in typical indoor environments and eliminates glare in optical or camera-adjacent builds.\u003c\/div\u003e\n\u003cdiv\u003e\n\u003cspan class=\"hdiy-icon\"\u003e📐\u003c\/span\u003e\u003cstrong\u003e0.5 Module, 25 Teeth — Standard Metric Pitch\u003c\/strong\u003e\u003cbr\u003eModule 0.5 is one of the most widely used small-module standards in RC, robotics, and hobby CNC. With 25 teeth, the pitch diameter is exactly 12.5 mm, making gear ratio calculations and mesh center-distance layout straightforward for system designers.\u003c\/div\u003e\n\u003cdiv\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🎯\u003c\/span\u003e\u003cstrong\u003eThree Bore Options: 4 mm, 5 mm, 6 mm\u003c\/strong\u003e\u003cbr\u003eCovers the most common small motor shaft diameters — 4 mm suits many micro gear motors and RC motor shafts, 5 mm fits NEMA 17 stepper motor shafts and standard RC brushless motors, and 6 mm accommodates larger hobby motors and shaft couplings.\u003c\/div\u003e\n\u003cdiv\u003e\n\u003cspan class=\"hdiy-icon\"\u003e📦\u003c\/span\u003e\u003cstrong\u003eFlexible Pack Quantities from 1 to 20 Pieces\u003c\/strong\u003e\u003cbr\u003eOrder a single gear for a one-off repair or prototype, or stock up with 5-, 10-, or 20-piece packs for production runs, classroom robotics kits, or keeping spares on the bench. Per-unit cost decreases with larger pack sizes.\u003c\/div\u003e\n\u003cdiv\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🔄\u003c\/span\u003e\u003cstrong\u003eDirect Mesh with 0.5 Mod Racks and Spur Gears\u003c\/strong\u003e\u003cbr\u003eFully interchangeable with any other 0.5-module spur gear or rack in your drive train. Use as a motor pinion driving a larger spur gear for speed reduction, or pair with a 0.5 mod rack for linear motion conversion in pen plotters and slide mechanisms.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\n\u003cdiv class=\"hdiy-table-wrap\"\u003e\n\u003ch2\u003e📐 Technical Specifications — 0.5 Mod Spur Pinion Gear\u003c\/h2\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth\u003eModule (Mod)\u003c\/th\u003e\n\u003ctd\u003e0.5\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eNumber of Teeth\u003c\/th\u003e\n\u003ctd\u003e25 T\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003ePitch Diameter\u003c\/th\u003e\n\u003ctd\u003e12.5 mm (0.492 in)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eOuter (Tip) Diameter\u003c\/th\u003e\n\u003ctd\u003eApprox. 13.5 mm (0.531 in)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eBore Diameter\u003c\/th\u003e\n\u003ctd\u003e4 mm \/ 5 mm \/ 6 mm (see variant options)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eHub Style\u003c\/th\u003e\n\u003ctd\u003eStepped hub\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eMaterial\u003c\/th\u003e\n\u003ctd\u003eCarbon steel\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eSurface Finish\u003c\/th\u003e\n\u003ctd\u003eBlack oxide\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eGear Type\u003c\/th\u003e\n\u003ctd\u003eSpur gear (straight tooth)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003ePressure Angle\u003c\/th\u003e\n\u003ctd\u003eSee variant options\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\u003ePack Quantity\u003c\/th\u003e\n\u003ctd\u003e1 \/ 2 \/ 3 \/ 5 \/ 10 \/ 20 pcs (select above)\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 correct bore diameter for my motor shaft?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eMeasure the outer diameter of your motor or drive shaft with a caliper. Select the bore option that matches: 4 mm for micro gear motors and small RC motor shafts, 5 mm for NEMA 17 stepper motors and standard brushless RC motors, or 6 mm for larger hobby motors and shaft couplings. The bore should be a close sliding fit on the shaft — not loose — so the set screw can clamp it securely.\u003c\/p\u003e\u003c\/div\u003e\n\u003c\/details\u003e\n\n\u003cdetails\u003e\n\u003csummary\u003eWhat does \"0.5 module\" mean, and will this gear mesh with my existing gears?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eModule (Mod) is the metric standard for gear tooth size, defined as pitch diameter divided by number of teeth. A 0.5 module gear has a tooth pitch of approximately 1.571 mm (π × 0.5 mm). This gear will mesh correctly with any other 0.5-module spur gear or rack, regardless of tooth count, as long as the pressure angle also matches (typically 20° for standard metric gears). It will NOT mesh correctly with gears of a different module.\u003c\/p\u003e\u003c\/div\u003e\n\u003c\/details\u003e\n\n\u003cdetails\u003e\n\u003csummary\u003eWhat is the center distance between this gear and a mating gear?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eThe center distance between two meshing spur gears equals half the sum of their pitch diameters: C = (D1 + D2) \/ 2. For this 25-tooth, 0.5-module gear, the pitch diameter is 12.5 mm. If it meshes with a 50-tooth, 0.5-module gear (pitch diameter 25 mm), the center distance would be (12.5 + 25) \/ 2 = 18.75 mm. Use this formula to lay out your gear train accurately.\u003c\/p\u003e\u003c\/div\u003e\n\u003c\/details\u003e\n\n\u003cdetails\u003e\n\u003csummary\u003eHow does the black oxide finish affect corrosion resistance?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eBlack oxide is a conversion coating that provides mild corrosion resistance suitable for indoor, low-humidity environments. It is not equivalent to zinc plating or stainless steel in wet or outdoor conditions. For applications exposed to moisture, splashing, or outdoor use, apply a light coat of machine oil or grease to the gear teeth and bore after installation to extend service life.\u003c\/p\u003e\u003c\/div\u003e\n\u003c\/details\u003e\n\n\u003cdetails\u003e\n\u003csummary\u003eWhat is the \"step\" or stepped hub, and why does it matter?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eThe stepped hub is a raised cylindrical boss on one or both faces of the gear that extends the bore length beyond the gear's face width. This longer bore engagement gives the set screw more clamping surface on the shaft, reducing the chance of the gear spinning or shifting axially under torque. It also makes it easier to position the gear at a precise axial location on the shaft by using the step as a reference shoulder.\u003c\/p\u003e\u003c\/div\u003e\n\u003c\/details\u003e\n\n\u003cdetails\u003e\n\u003csummary\u003eCan I use this gear in a speed-reduction stage, and what gear ratios are achievable?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eYes — this 25-tooth pinion is commonly used as the driving (input) gear in a reduction stage. The gear ratio equals the number of teeth on the driven gear divided by 25. For example, pairing with a 50-tooth gear gives a 2:1 reduction; a 75-tooth gear gives 3:1. All mating gears must be 0.5 module. This makes the gear well-suited for stepper motor drives, RC car differentials, and small gearbox stages where torque multiplication is needed.\u003c\/p\u003e\u003c\/div\u003e\n\u003c\/details\u003e\n\n\u003cdetails\u003e\n\u003csummary\u003eHow do I secure the gear to the shaft — does it come with a set screw?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eThe gear is designed for set-screw retention. Check whether a set screw is pre-installed in the hub; if not, a standard M2 or M3 grub screw (depending on hub size) fits the threaded hole in the hub. For shafts without a flat, apply medium-strength thread-locking compound to the set screw before tightening to prevent loosening under vibration. For shafts with a D-flat or keyway, align the set screw with the flat for maximum retention.\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 diameter and quantity 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 correct bore diameter for my motor shaft?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Measure the outer diameter of your motor or drive shaft with a caliper. Select the bore option that matches: 4 mm for micro gear motors and small RC motor shafts, 5 mm for NEMA 17 stepper motors and standard brushless RC motors, or 6 mm for larger hobby motors and shaft couplings.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What does '0.5 module' mean, and will this gear mesh with my existing gears?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Module (Mod) is the metric standard for gear tooth size, defined as pitch diameter divided by number of teeth. A 0.5 module gear has a tooth pitch of approximately 1.571 mm. This gear will mesh correctly with any other 0.5-module spur gear or rack with a matching pressure angle. It will NOT mesh correctly with gears of a different module.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What is the center distance between this gear and a mating gear?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Center distance = (D1 + D2) \/ 2. For this 25-tooth, 0.5-module gear, pitch diameter is 12.5 mm. Meshing with a 50-tooth, 0.5-module gear (pitch diameter 25 mm) gives a center distance of 18.75 mm.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"How does the black oxide finish affect corrosion resistance?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Black oxide provides mild corrosion resistance suitable for indoor, low-humidity environments. For applications exposed to moisture or outdoor use, apply a light coat of machine oil or grease to the gear teeth and bore after installation.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What is the stepped hub, and why does it matter?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"The stepped hub is a raised cylindrical boss that extends the bore length beyond the gear face width, giving the set screw more clamping surface on the shaft and reducing the chance of the gear spinning or shifting axially under torque.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Can I use this gear in a speed-reduction stage, and what gear ratios are achievable?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Yes. The gear ratio equals the number of teeth on the driven gear divided by 25. Pairing with a 50-tooth gear gives 2:1 reduction; a 75-tooth gear gives 3:1. All mating gears must be 0.5 module.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"How do I secure the gear to the shaft — does it come with a set screw?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"The gear is designed for set-screw retention. A standard M2 or M3 grub screw fits the threaded hole in the hub. For shafts without a flat, apply medium-strength thread-locking compound to prevent loosening under vibration.\"\n      }\n    }\n  ]\n}\n\u003c\/script\u003e","brand":"HomeDIYer","offers":[{"title":"4mm \/ 25 T \/ 1 Pcs","offer_id":52441828163858,"sku":"BGMGLCDPJ00037x1","price":6.95,"currency_code":"USD","in_stock":true},{"title":"4mm \/ 25 T \/ 2 Pcs","offer_id":52441828196626,"sku":"BGMGLCDPJ00037x2","price":11.52,"currency_code":"USD","in_stock":true},{"title":"4mm \/ 25 T \/ 3 Pcs","offer_id":52441828229394,"sku":"BGMGLCDPJ00037x3","price":16.48,"currency_code":"USD","in_stock":true},{"title":"4mm \/ 25 T \/ 5 Pcs","offer_id":52441828262162,"sku":"BGMGLCDPJ00037x5","price":26.56,"currency_code":"USD","in_stock":true},{"title":"4mm \/ 25 T \/ 10 Pcs","offer_id":52441828294930,"sku":"BGMGLCDPJ00037x10","price":51.63,"currency_code":"USD","in_stock":true},{"title":"4mm \/ 25 T \/ 20 Pcs","offer_id":52441828327698,"sku":"BGMGLCDPJ00037x20","price":101.8,"currency_code":"USD","in_stock":true},{"title":"5mm \/ 25 T \/ 1 Pcs","offer_id":52441828360466,"sku":"BGMGLCDPJ00038x1","price":6.95,"currency_code":"USD","in_stock":true},{"title":"5mm \/ 25 T \/ 2 Pcs","offer_id":52441828393234,"sku":"BGMGLCDPJ00038x2","price":11.52,"currency_code":"USD","in_stock":true},{"title":"5mm \/ 25 T \/ 3 Pcs","offer_id":52441828426002,"sku":"BGMGLCDPJ00038x3","price":16.48,"currency_code":"USD","in_stock":true},{"title":"5mm \/ 25 T \/ 5 Pcs","offer_id":52441828458770,"sku":"BGMGLCDPJ00038x5","price":26.56,"currency_code":"USD","in_stock":true},{"title":"5mm \/ 25 T \/ 10 Pcs","offer_id":52441828491538,"sku":"BGMGLCDPJ00038x10","price":51.63,"currency_code":"USD","in_stock":true},{"title":"5mm \/ 25 T \/ 20 Pcs","offer_id":52441828524306,"sku":"BGMGLCDPJ00038x20","price":101.8,"currency_code":"USD","in_stock":true},{"title":"6mm \/ 25 T \/ 1 Pcs","offer_id":52441828557074,"sku":"BGMGLCDPJ00039x1","price":6.95,"currency_code":"USD","in_stock":true},{"title":"6mm \/ 25 T \/ 2 Pcs","offer_id":52441828589842,"sku":"BGMGLCDPJ00039x2","price":11.52,"currency_code":"USD","in_stock":true},{"title":"6mm \/ 25 T \/ 3 Pcs","offer_id":52441828622610,"sku":"BGMGLCDPJ00039x3","price":16.48,"currency_code":"USD","in_stock":true},{"title":"6mm \/ 25 T \/ 5 Pcs","offer_id":52441828655378,"sku":"BGMGLCDPJ00039x5","price":26.56,"currency_code":"USD","in_stock":true},{"title":"6mm \/ 25 T \/ 10 Pcs","offer_id":52441828688146,"sku":"BGMGLCDPJ00039x10","price":51.63,"currency_code":"USD","in_stock":true},{"title":"6mm \/ 25 T \/ 20 Pcs","offer_id":52441828720914,"sku":"BGMGLCDPJ00039x20","price":101.8,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0884\/8936\/1682\/files\/Picture3of5_6e18c1d0-233e-4ec5-bd3c-ebe991d4cd4d.jpg?v=1783583147","url":"https:\/\/homediyer.com\/products\/0-5-mod-pinion-gear-black-steel-spur-gears-with-step-transmission-gear-25-teeth","provider":"HomeDIYer","version":"1.0","type":"link"}