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When a stripped or mismatched gear brings your build to a halt, you need a replacement you can trust to mesh perfectly and hold up under load. These Module 3 spur gears are engineered for makers, machinists, and automation engineers who demand dimensional accuracy and consistent torque transfer across a wide range of tooth counts.
Each gear is machined from 45# medium-carbon steel, delivering a solid balance of strength and machinability. The module (pitch) is 3 mm, with a standard 20° pressure angle. Tooth counts span from 12 to 75 teeth, giving pitch circle diameters that range from approximately 36 mm (1.42 in) for 12T up to 225 mm (8.86 in) for 75T. Bore diameter varies by tooth count — see variant options for exact bore dimensions.
Typical use cases include DIY CNC router axis drives, 3D printer extruder gear trains, robotic arm joint transmission, electric motor reduction stages, and custom gearbox builds where off-the-shelf module 3 spur pinion gears are required for precise speed and torque ratios.
45# Steel Construction — Medium-carbon steel provides solid tensile strength and wear resistance for continuous-duty transmission applications.
Standard Module 3 / 20° Pressure Angle — Fully interchangeable with any Mod 3 mating gear or rack; no custom tooling required.
Wide Tooth Count Range (12–75T) — Select the exact gear ratio you need; covers pinion to mid-size driven gear applications in a single product line.
Machined Tooth Profile — Hobbed tooth form ensures smooth meshing, reduced backlash, and consistent load distribution across the full face width.
Machinable Bore — Supplied with a standard bore; easily re-bored, keyed, or set-screwed to match your shaft diameter on a lathe or mill.
Single-Piece or Multi-Pack Options — Available in 1 Pc per order; ideal for prototyping, replacement, or staged builds without over-ordering.
| Module (Pitch) | 3 mm |
|---|---|
| Pressure Angle | 20° |
| Tooth Count Range | 12 – 75 Teeth (see variant options) |
| Material | 45# Medium-Carbon Steel |
| Pitch Circle Diameter | Module × Teeth (e.g. 3 × 20T = 60 mm / 2.36 in) |
| Bore Diameter | See variant options |
| Face Width | See variant options |
| Hub Style | Plain bore (machinable) |
| Surface Finish | Natural steel / lightly oiled |
| Gear Type | External spur gear |
| Quantity per Order | 1 Pc |
Divide your desired gear ratio by the tooth count of your mating gear. For example, a 4:1 reduction with a 12-tooth pinion requires a 48-tooth driven gear. Use the pitch circle diameter formula (PCD = Module × Teeth) to verify the center distance fits your housing before ordering.
Yes — any gear or rack with Module 3 and a 20° pressure angle will mesh correctly with these spur gears. Confirm both the module and pressure angle of your existing components before purchasing, as Module 2.5 or Module 4 gears are not interchangeable.
45# steel (equivalent to AISI 1045) has a typical tensile strength of approximately 600–700 MPa in the normalized condition. It is well-suited for moderate-to-high torque transmission in CNC, robotics, and motor drive applications. For extreme shock loads or very high-speed operation, consider heat-treated or alloy steel alternatives.
45# steel is not inherently corrosion-resistant. For outdoor or high-humidity environments, apply a light coat of grease or anti-rust oil during installation and re-apply periodically. If corrosion resistance is critical, consider stainless steel or nylon gear alternatives for your application.
Yes. The plain bore is machinable on a lathe or mill. You can enlarge the bore to match your shaft diameter, cut a keyway, or drill and tap for a set screw. Ensure sufficient wall thickness remains after machining — check the hub diameter for your selected tooth count before modifying.
Center distance = (Teeth on Gear 1 + Teeth on Gear 2) × Module ÷ 2. For example, a 20-tooth pinion meshing with a 40-tooth gear: (20 + 40) × 3 ÷ 2 = 90 mm. Use this formula to design your housing or bracket before machining.
A general-purpose gear grease (NLGI Grade 1 or 2) or a light machine oil works well for most indoor applications. Apply lubricant to the tooth flanks during assembly and re-lubricate at regular service intervals based on your duty cycle and operating speed.
