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When your motion-control build demands tight mesh tolerances and reliable torque transfer, a poorly fitted gear can derail the entire mechanism. Engineers, robotics hobbyists, and CNC makers who need a compact 0.5 Mod 20-tooth spur gear with a secure shaft fit will find this black oxide steel gear a dependable solution across a wide range of shaft diameters.
Each gear is machined from carbon steel and finished with a black oxide coating for corrosion resistance. The module is 0.5 with 20 teeth, giving an outer diameter of approximately 11 mm (0.43 in). Bore options span 4 mm, 5 mm, 6 mm, and 6.35 mm (1/4 in), covering the most common motor and shaft standards. A set screw is included on each gear for positive shaft retention without adhesives.
Typical use cases include small robotic arm joints requiring a 0.5 mod spur gear with set screw, compact CNC axis drives using a 20-tooth steel gear with 6 mm bore, and DIY clock or automaton mechanisms where a miniature black oxide spur gear keeps aesthetics clean while maintaining durability.
Each gear includes a radial set screw for positive shaft locking — no adhesive or press-fit required, making disassembly and repositioning straightforward.
The black oxide surface treatment provides mild corrosion resistance and reduces light reflection — suitable for indoor mechanical assemblies and light-duty outdoor enclosures.
Machined to 0.5 module standard, these gears mesh accurately with any Mod 0.5 counterpart — rack, pinion, or mating spur — for smooth, low-backlash power transmission.
Available in 4 mm, 5 mm, 6 mm, and 6.35 mm (1/4 in) bore diameters to match the most common motor shaft and hobby shaft standards without custom machining.
Manufactured from carbon steel for a balance of machinability, tensile strength, and wear resistance — appropriate for moderate-load, moderate-speed drive applications.
Order as 1, 3, 5, or 10 pieces per variant to match your project scale — from single-unit prototyping to small-batch production runs.
| Module (Mod) | 0.5 |
|---|---|
| Number of Teeth | 20 |
| Outer Diameter (OD) | Approx. 11 mm (0.43 in) |
| Pitch Diameter | 10 mm (0.39 in) |
| Bore Diameter | 4 mm / 5 mm / 6 mm / 6.35 mm (1/4 in) — See variant options |
| Hub / Face Width | See variant options |
| Material | Carbon Steel |
| Surface Finish | Black Oxide |
| Shaft Retention | Set Screw (included) |
| Pressure Angle | 20° |
| Pack Quantity | 1 / 3 / 5 / 10 pcs — See variant options |
Measure your motor or drive shaft diameter with a caliper. Select the bore that matches: 4 mm for small stepper and hobby motors, 5 mm for common NEMA 17 stepper shafts, 6 mm for many DC gear motors, and 6.35 mm (1/4 in) for standard US hobby and servo shafts. The set screw accommodates minor shaft tolerance variation but is not a substitute for a correct bore match.
Yes. Any gear, rack, or pinion manufactured to the 0.5 module (Mod 0.5) standard will mesh correctly with this gear. Confirm the module and pressure angle (20°) of your mating component before assembly.
Black oxide provides mild corrosion resistance suitable for dry or lightly humid indoor environments. For outdoor or high-moisture applications, apply a light machine oil or grease to the gear surface periodically. Black oxide is not equivalent to zinc plating or stainless steel in corrosion protection.
Exact load ratings depend on application conditions (lubrication, duty cycle, mating gear material). As a conservative guideline for carbon steel Mod 0.5 gears, these are suited for low-to-moderate torque applications typical of robotics, small CNC axes, and instrumentation drives. Contact us to confirm suitability for high-cycle or high-load scenarios.
The set screw is typically driven with a hex (Allen) key. The exact set screw thread size varies by bore variant — contact us to confirm the wrench size for your specific bore option before assembly.
These gears can operate dry at low speeds and light loads, but applying a thin film of gear grease or machine oil at the mesh contact point will significantly extend service life and reduce noise, especially in continuous-duty or higher-speed applications.
Multi-piece packs (3, 5, or 10 pcs) are cost-effective for builds requiring matched gear pairs, redundancy spares, or small-batch production. The per-unit price decreases with larger quantities, making them practical for prototyping iterations where gears may be replaced or repositioned.
