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Finding a 0.5 module spur gear with the right tooth count and bore to match your motor shaft is a common challenge for robotics builders, RC hobbyists, and small-machine designers. This 40-tooth brass pinion gear covers bore sizes from 4 mm to 12 mm, giving engineers and makers a single SKU family that fits the widest range of compact drive shafts without custom machining.
Each gear is machined from solid brass, delivering a balance of machinability, moderate corrosion resistance, and low-noise meshing. The module is 0.5 (metric), tooth count is 40T, and bore options span 4 mm to 12 mm (approximately 0.157 in to 0.472 in). At 0.5 module with 40 teeth, the pitch diameter is approximately 20 mm (~0.79 in), making it slightly larger than a 32T variant and suited to applications requiring a lower gear ratio or higher torque multiplication on the output side.
Typical use cases include servo-driven robotic arm joints using a 0.5 mod 40-tooth spur gear for stage reduction, RC buggy or crawler transmission pinion replacement where a larger tooth count is needed for a specific ratio, and compact automation gearbox stages where a brass pinion gear with a 4 mm to 12 mm bore is specified. Available in packs of 1, 2, 5, or 10 pieces to support prototyping through small-batch production runs.
| Module | 0.5 (Metric) |
|---|---|
| Tooth Count | 40T |
| Bore Diameter | 4 / 5 / 6 / 6.35 / 7 / 8 / 10 / 12 mm — See variant options |
| Pitch Diameter | ~20 mm (~0.79 in) |
| Pressure Angle | 20° (standard) |
| Material | Brass |
| Finish | Natural brass (uncoated) |
| Gear Type | Spur (straight tooth) |
| Face Width | See variant options |
| Hub / Boss | See variant options |
| Keyway / Set Screw | See variant options |
| Pack Quantity | 1 / 2 / 5 / 10 PCS — See variant options |
The critical parameter is the module. This gear is Module 0.5 (metric). Any mating spur gear, rack, or pinion must also be Module 0.5 for correct tooth engagement. Tooth count (40T) affects gear ratio only — not meshing compatibility. A 0.5 Mod gear with any tooth count will mesh with this gear as long as the module matches.
Measure your shaft diameter with calipers. Available bores are 4, 5, 6, 6.35, 7, 8, 10, and 12 mm. The 6.35 mm bore corresponds to a 1/4-inch shaft, common in North American hobby motors. The 12 mm bore suits larger servo or stepper motor shafts. Select the bore that matches your shaft — a loose fit causes runout and noise; a tight fit requires careful pressing or a set screw.
Both gears share the same 0.5 module and will mesh with each other. The 40T gear has a larger pitch diameter (~20 mm vs ~16 mm for 32T), which changes the gear ratio when paired with a pinion or spur of a different tooth count. A higher tooth count on the driven gear produces more torque and lower output speed; a higher tooth count on the driving gear produces higher speed and lower torque.
Brass is well-suited for low-to-medium torque applications such as RC car pinions, servo-driven robotic joints, and light automation stages. It offers quieter operation and easier machining than steel. For high-torque or high-RPM industrial drives, a steel or hardened alloy gear may be more appropriate. If you are unsure about load requirements, contact us to confirm suitability.
Brass has moderate natural corrosion resistance and performs reliably in typical indoor and light outdoor environments. It is not recommended for continuous immersion in water or exposure to highly corrosive chemicals. For wet-environment applications, applying a light gear lubricant will extend service life.
Pinion gears are wear items, especially in high-cycle applications like RC racing or repetitive robotic movements. Ordering a 5- or 10-pack ensures you have spares on hand for quick replacement without waiting for reshipment. Multi-packs also offer a lower per-unit cost compared to single-piece orders.
Set screw and keyway availability varies by variant. Please check the variant detail page or contact us to confirm the shaft retention method for your selected bore size before ordering.
Yes, for light-duty automation and positioning stages where a 0.5 mod 40-tooth brass spur gear is specified. Brass is commonly used in instrumentation and light automation due to its dimensional stability and low friction. For heavy-duty CNC axes or high-load stages, consult your load and speed requirements before selecting brass over steel.
