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When a stripped or undersized gear brings your motor-driven project to a halt, finding a replacement that fits your exact shaft bore and step diameter is the real challenge. Whether you are a robotics builder, CNC hobbyist, or mechanical engineer prototyping a drive system, these 1 Mod 25 Teeth Spur Gears with set screws are engineered to drop into your build without modification.
Each gear is machined from carbon steel with a black oxide finish for corrosion resistance and a clean, professional appearance. The module is 1 (Mod 1), tooth count is 25, and the step (hub) diameter is available in 20 mm (~0.79 in) or 22 mm (~0.87 in). Hole diameters range from 5 mm (~0.20 in) up to 16 mm (~0.63 in), with keyway and D-type bore options for positive shaft engagement. Set screws are included for secure, tool-accessible locking.
Typical use cases include DC motor gearbox assemblies requiring a 1 mod 25 tooth replacement gear, small CNC axis drives where a keyed spur gear ensures zero-slip torque transfer, and robotics joint mechanisms that need a compact D-bore spur gear for flat-shaft motors.
Module 1 Standard Pitch
Mod 1 tooth profile meshes precisely with any standard Mod 1 rack or mating gear, ensuring smooth, low-noise power transmission in motor drive trains.
Set Screw Locking
Integrated set screw(s) allow tool-free shaft positioning and secure locking without permanent modification, making installation and removal straightforward.
Black Oxide Carbon Steel
The black oxide surface treatment provides a layer of corrosion resistance and reduces light reflection, suitable for indoor mechanical assemblies and light-duty outdoor enclosures.
Wide Bore Selection
Available in round bores (5–16 mm), keyway bores (3×1.4 mm, 4×1.8 mm, 5×2.3 mm), and D-type bores (5–12 mm flat), covering the most common motor shaft standards.
Two Step Diameter Options
Choose between a 20 mm or 22 mm hub (step) diameter to match your housing bore or bearing seat, reducing the need for custom spacers.
Single or 3-Pack Quantities
Order as a single piece for a direct replacement or as a 3-pack for multi-axis builds, spare inventory, or prototype iterations — all at a consistent per-unit specification.
| Module | 1 (Mod 1) |
|---|---|
| Number of Teeth | 25 |
| Pressure Angle | 20° |
| Step (Hub) Diameter | 20 mm / 22 mm (see variant options) |
| Hole Diameter (Bore) | 5 mm – 16 mm round; keyway and D-type options available (see variant options) |
| Keyway Sizes Available | 3×1.4 mm, 4×1.8 mm, 5×2.3 mm (see variant options) |
| D-type Bore Sizes Available | 5×4.5 mm, 6×5 mm, 6×5.5 mm, 8×7 mm, 8×7.5 mm, 10×9 mm, 12×10.5 mm, 12×11 mm (see variant options) |
| Material | Carbon Steel |
| Surface Finish | Black Oxide |
| Fastening Method | Set Screw |
| Pitch Diameter | 25 mm (Module × Teeth = 1 × 25) |
| Outside Diameter | Approximately 27 mm (~1.06 in) |
| Quantity per Order | 1 pcs or 3 pcs (see variant options) |
| Weight (per piece) | See variant options |
Measure your motor shaft diameter with a caliper. Select the bore option that matches exactly — for example, a 6 mm shaft needs the "Bore 6mm" variant. If your shaft has a flat (D-cut), choose the corresponding D-type bore option. If your shaft has a keyway slot, select the keyway bore variant whose keyway width and depth match your shaft's key dimensions.
The step (hub) diameter refers to the outer diameter of the gear's hub section, which may seat into a bearing or housing bore. Choose 20 mm if your housing or bearing inner diameter is 20 mm, and 22 mm if it is 22 mm. This dimension does not affect the gear mesh — both options have the same Mod 1, 25-tooth tooth profile.
Yes. Any Mod 1 gear, rack, or pinion with a standard 20° pressure angle will mesh correctly with this gear. Confirm that your mating component is also Module 1 — mixing modules (e.g., Mod 0.8 or Mod 1.5) will result in incorrect meshing and accelerated wear.
Black oxide provides a mild level of corrosion resistance compared to bare steel, but it is not equivalent to zinc plating or stainless steel. For outdoor or high-humidity applications, we recommend applying a light machine oil or grease to the gear surface as an additional protective measure.
The set screw provides adequate holding force for light-to-medium duty motor applications typical of Mod 1 gears. For high-torque applications, the keyway bore variants offer significantly better torque transfer by distributing load across the key rather than relying solely on the set screw's point contact. D-type bores also improve anti-rotation performance over plain round bores.
Yes — select your preferred Hole Diameter (bore type and size) and Step Diameter (20 mm or 22 mm) independently using the variant selectors above. Not all bore-and-step combinations are listed; if you need a specific combination not shown, please contact us to confirm availability.
For a Module 1 gear with 25 teeth: Pitch Diameter = Module × Teeth = 1 × 25 = 25 mm. Outside Diameter = (Teeth + 2) × Module = 27 mm (~1.06 in). These values are standard for Mod 1 and can be used to calculate center distance when pairing with a mating gear.
