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When a slipping or undersized gear brings your CNC router, 3D printer, or automation project to a halt, you need a replacement you can trust. These 1.5 Module 45# carbon steel spur gears are engineered for makers, robotics builders, and mechanical engineers who demand accurate tooth profiles and reliable bore fits without custom machining.
Each gear is machined from 45# medium-carbon steel, offering a good balance of hardness and machinability. The range covers 12 to 27 teeth (12T–27T) with an outer diameter that scales proportionally per the 1.5 Mod standard (typically 21 mm–43.5 mm / 0.83"–1.71"). Bore options span 6 mm to 18 mm (0.24"–0.71"), with select variants featuring a precision-cut keyway (4 mm or 5 mm / 6 mm) for positive torque transmission without set-screw slippage.
These spur gears are well-suited for stepper motor pinion drives in CNC machines, gear reduction stages in conveyor and feeder systems, and shaft-to-shaft power transmission in robotics and automation rigs — anywhere a compact, metric-pitch gear is needed for a long-tail search like "1.5 mod steel spur gear with keyway" or "45 steel pinion gear bore 12mm."
| Module (Mod) | 1.5 |
|---|---|
| Material | 45# Carbon Steel |
| Number of Teeth | 12T – 27T (see variant options) |
| Bore Diameter | 6 mm – 18 mm (see variant options) |
| Keyway | 4 mm or 5 mm / 6 mm (keyway variants only; see variant options) |
| Outer Diameter (OD) | Approx. 21 mm – 43.5 mm (scales with tooth count at 1.5 Mod) |
| Pressure Angle | 20° |
| Tooth Profile | Involute, metric standard |
| Finish | See variant options |
| Hub / Face Width | See variant options |
| Compatible Pitch | 1.5 Module (metric) |
The tooth count determines your gear ratio. Divide the driven gear's tooth count by the driving gear's tooth count to get the ratio. For example, a 12T pinion driving a 24T gear gives a 2:1 reduction — the output shaft turns at half the speed but with twice the torque. Use a smaller tooth count (12T–15T) for higher speed, and a larger count (20T–27T) when you need more torque output.
Measure your motor shaft diameter with a calliper before ordering. Common NEMA 17 stepper shafts are 5 mm, NEMA 23 shafts are typically 6.35 mm or 8 mm, and NEMA 34 shafts are often 12.7 mm or 14 mm. Select the bore that matches your shaft — a bore that is too large will cause runout and vibration. If your shaft has a flat or key, choose a keyway variant for a positive fit.
For light-duty or low-torque applications (e.g., 3D printer extruder drives), a plain bore secured with a set screw is usually sufficient. For higher-torque applications — CNC axis drives, conveyor feeds, or any system with reversing loads — a keyway variant is strongly recommended. The key prevents the gear from rotating on the shaft under shock loads, which a set screw alone cannot reliably prevent.
45# carbon steel (roughly equivalent to AISI 1045) has a tensile strength of approximately 600–800 MPa in the normalised condition, making it suitable for moderate-load mechanical drives such as CNC routers, light conveyor systems, and robotics joints. For very high-load or high-speed industrial applications, consider whether a hardened or alloy steel gear would be more appropriate for your specific torque and duty-cycle requirements.
Yes — as long as your existing rack or mating gear is also 1.5 Module with a 20° pressure angle (the most common metric standard), these gears will mesh correctly. Module and pressure angle must match between mating gears; tooth count only affects the gear ratio, not compatibility. If you are unsure of your existing gear's module, measure the outer diameter (mm) and divide by (number of teeth + 2) — the result should be close to 1.5.
45# carbon steel is not inherently corrosion-resistant. In dry indoor environments (CNC enclosures, electronics bays, robotics frames) the gears will perform well without additional treatment. If your application involves moisture, coolant mist, or outdoor exposure, apply a light machine oil or grease to the tooth faces, or consider a protective coating. For wet or chemically aggressive environments, a stainless steel or engineering plastic gear may be a better long-term choice.
Centre distance (C) = Module × (Teeth on Gear 1 + Teeth on Gear 2) ÷ 2. For example, a 12T pinion meshing with a 24T gear: C = 1.5 × (12 + 24) ÷ 2 = 1.5 × 18 = 27 mm. Use this formula to set your shaft spacing accurately and avoid binding or excessive backlash.
