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When your CNC machine, robotic arm, or industrial drive system demands consistent torque transfer without slippage or premature wear, the choice of pinion gear matters. Engineers and makers working with high-load transmission assemblies need a Mod 4 spur gear that holds tight tolerances across extended duty cycles — these 45# carbon steel gears are built for exactly that application.
Each gear is machined from 45# medium-carbon steel, offering a balance of hardness and machinability suited for power transmission components. The tooth thickness is a fixed 35mm (~1.38 in), with a Module 4 pitch. Tooth counts range from 10T to 39T, covering pitch circle diameters from approximately 40mm (~1.57 in) for the 10T up to approximately 156mm (~6.14 in) for the 39T variant. Bore diameter varies by tooth count — see variant options for exact bore specs.
These Mod 4 pinion gears are well-suited for CNC router Z-axis and rack-and-pinion drives, rotary indexing tables and servo motor output shafts, and custom gearbox assemblies in automation and conveyor systems where a reliable steel spur gear transmission component is required.
| Module | 4 (Mod 4) |
|---|---|
| Material | 45# Carbon Steel |
| Face Width (Tooth Thickness) | 35mm (~1.38 in) |
| Tooth Count Range | 10T – 39T (30 variants) |
| Pitch Circle Diameter | See variant options (Module × Teeth) |
| Bore Diameter | See variant options |
| Tooth Profile | Standard Involute |
| Pressure Angle | 20° |
| Surface Finish | See variant options |
| Quantity per Order | 1 Pcs |
Select your tooth count based on the gear ratio you need. Divide the driven gear's tooth count by the driving gear's tooth count to get the ratio. For example, pairing a 10T pinion with a 30T gear gives a 3:1 reduction. Smaller tooth counts (10T–15T) suit high-reduction, high-torque setups; larger counts (30T–39T) are better for lower reduction or speed-matching applications.
Bore diameter varies by tooth count and is listed in the variant options on this page. Always verify the bore size matches your motor or shaft diameter before ordering. If you need a custom bore, the steel material is machinable for post-purchase boring by a machine shop.
Yes. All gears in this listing use Module 4 pitch with a standard 20° pressure angle involute tooth profile, which is fully compatible with any other Mod 4 rack, pinion, or spur gear of the same module and pressure angle. Do not mix with Mod 3 or Mod 5 components — module must match for proper meshing.
45# carbon steel (equivalent to AISI 1045) has a tensile strength of approximately 600–800 MPa in the normalized condition, making it a solid choice for moderate-to-heavy duty gear applications. It is commonly used in industrial gearboxes, machine tool drives, and automation systems. For very high-shock or extreme-load environments, consider whether a hardened or alloy steel variant better suits your torque requirements.
Carbon steel is susceptible to surface oxidation if left unprotected in humid or wet environments. For indoor CNC and automation use, applying a light machine oil or grease to the gear teeth during operation provides adequate protection and lubrication. For outdoor or high-moisture environments, consider adding a protective coating or using stainless steel alternatives.
Yes, these Mod 4 pinion gears are commonly used with both stepper and servo motors in CNC and robotics builds. Confirm that the bore diameter of your selected tooth count matches your motor shaft diameter. A keyway or set-screw bore style may be required depending on your motor shaft — check the variant details or contact us to confirm bore configuration.
Pitch circle diameter (PCD) for a Mod 4 gear is calculated as: PCD = Module × Tooth Count. For example: 4 × 10T = 40mm PCD; 4 × 20T = 80mm PCD; 4 × 39T = 156mm PCD. Use this formula to calculate center distance between mating gears: Center Distance = (PCD₁ + PCD₂) / 2.
