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When a slipping or undersized gear stalls your CNC router, robotics arm, or automation drive mid-cycle, the cost is more than downtime — it's lost accuracy and rework. Engineers, makers, and small-batch manufacturers who need a reliable, drop-in pinion gear for Mod 4 drive trains will find this steel spur gear series purpose-built for the task.
Each gear is machined from carbon steel and features a flat (spur) tooth profile with a Module 4 pitch. The series spans 10 to 24 teeth, yielding outer diameters from approximately 48 mm (≈1.89 in) at 10T up to 104 mm (≈4.09 in) at 24T, with a standard bore sized to suit common motor shafts — confirm your shaft diameter against the variant options before ordering.
Typical applications include CNC rack-and-pinion linear drives, stepper and servo motor output stages, conveyor indexing systems, and open-frame robotics joints where a Mod 4 steel pinion gear with consistent tooth geometry is required for repeatable positioning.
Machined from carbon steel for the strength and wear resistance needed in continuous-duty drive applications, including CNC and robotics.
Standard Mod 4 involute tooth geometry ensures accurate meshing with any compatible Mod 4 rack or mating gear, minimizing backlash in precision drives.
Select from 15 tooth-count variants (10T through 24T) to dial in your exact gear ratio without sourcing from multiple suppliers.
OD scales predictably with tooth count (OD = Module × Teeth + 2 × Module), giving you a reliable reference for envelope clearance in tight assemblies.
The flat spur (straight-tooth) design transmits torque efficiently on parallel shafts — ideal for stepper and servo motor pinion applications where axial load is minimal.
Standard Mod 4 dimensions mean these gears serve as direct replacements for worn pinions in existing Mod 4 drive systems without custom machining.
| Module (Mod) | 4 |
|---|---|
| Tooth Count Range | 10T – 24T (15 variants) |
| Outer Diameter Range | 48 mm – 104 mm (1.89 in – 4.09 in) |
| Tooth Profile | Involute spur (flat / straight tooth) |
| Material | Carbon steel |
| Pressure Angle | 20° (standard involute) |
| Bore Diameter | See variant options |
| Hub / Face Width | See variant options |
| Finish | See variant options |
| Compatible Module | Mod 4 rack, ring gear, or mating spur gear |
| Weight | See variant options |
Your gear ratio is determined by dividing the tooth count of the driven gear by the tooth count of the driving pinion. For example, pairing a 10T pinion with a 40T gear gives a 4:1 reduction. Select a tooth count that achieves your target ratio while keeping the outer diameter within your assembly envelope. The OD formula for Mod 4 is: OD (mm) = 4 × (Teeth + 2).
Module (Mod) is the metric standard for gear tooth size — it equals the pitch diameter divided by the number of teeth. Mod 4 gears will only mesh correctly with other Mod 4 gears or Mod 4 racks. They are not interchangeable with Mod 2, Mod 3, or imperial diametral-pitch gears. Check your existing gear's module marking or measure the tooth pitch before ordering.
Carbon steel spur gears in Mod 4 are well-suited for moderate-to-high torque CNC rack-and-pinion drives, stepper/servo motor output stages, and robotics joints operating at typical automation speeds. For very high-speed or shock-load applications, confirm the face width and bore specifications of your chosen variant against your torque and RPM requirements.
Carbon steel has moderate corrosion resistance. For outdoor, humid, or washdown environments, we recommend applying a light machine oil or grease coating during installation and re-lubricating periodically. If your application demands higher corrosion resistance, consider stainless steel alternatives or apply a protective coating after installation.
Bore diameter varies by variant. Please check the variant options or contact us to confirm the bore size matches your motor or shaft diameter before ordering. Many Mod 4 pinions in this size range use bores from approximately 8 mm to 20 mm, but verify against the specific variant you select.
Yes — as long as your existing system uses Mod 4 gearing, these pinions serve as direct replacements. Match the tooth count, bore diameter, and face width of your worn gear to the appropriate variant. Standard Mod 4 tooth geometry ensures correct meshing without additional machining in most cases.
Spur gears (like these) have straight teeth parallel to the shaft axis. They are simpler, less expensive, and generate no axial thrust — making them ideal for parallel-shaft drives where axial load management is not required. Helical gears offer quieter operation and higher load capacity but introduce axial forces that require thrust bearings. For most CNC and robotics pinion applications, spur gears are the practical choice.
