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When a worn or undersized sprocket causes chain skip, premature wear, or misalignment on your drive system, finding an exact-fit replacement is critical. This 04C pilot bore roller chain sprocket is designed for DIYers, machine builders, and repair technicians who need a dimensionally accurate, drop-in sprocket without the cost of custom machining.
Each sprocket is machined from steel and is available in 17T, 18T, 19T, and 20T tooth counts to match your existing chain drive ratio. Bore options range from 5 mm (0.20 in) to 20 mm (0.79 in), including plain round bores and keyed bores with standard keyway dimensions (3×1.4 mm, 4×1.8 mm, 5×2.3 mm, and 6×2.8 mm). The 04C designation corresponds to ANSI #25 / ISO 04C chain with a 6.35 mm (0.25 in) pitch.
Typical applications include small conveyor drives, go-kart and mini-bike chain drives, robotics and automation platforms, agricultural equipment auxiliary drives, and general-purpose power transmission where a compact 04C chain sprocket is required. Sold in packs of 1, 3, or 5 pieces for single-unit replacement or multi-machine maintenance stock.
| Chain Standard | 04C / ANSI #25 |
|---|---|
| Chain Pitch | 6.35 mm (0.25 in) |
| Tooth Count Options | 17T, 18T, 19T, 20T |
| Bore Type | Plain round bore / Keyed bore (see variant options) |
| Bore Diameter Range | 5 mm – 20 mm (0.20 – 0.79 in) |
| Keyway Dimensions | 3×1.4 mm / 4×1.8 mm / 5×2.3 mm / 6×2.8 mm (see variant options) |
| Material | Steel |
| Finish | See variant options |
| Hub Diameter | See variant options |
| Overall Thickness | See variant options |
| Pack Quantity | 1 pc / 3 pcs / 5 pcs |
| Weight (per piece) | See variant options |
The tooth count determines your drive ratio. Divide the driven sprocket teeth by the driver sprocket teeth to get the reduction ratio. For example, a 17T driver paired with a 34T driven sprocket gives a 2:1 reduction. Match the tooth count to your existing setup or calculate the ratio you need for your target output speed.
These sprockets are designed for 04C roller chain, which is equivalent to ANSI #25 chain with a 6.35 mm (0.25 in) pitch. Do not use with 08B, #35, or other chain sizes — the tooth profile and pitch must match exactly to avoid accelerated wear and chain derailment.
Measure your shaft diameter with a caliper. Select the bore option that matches your shaft size. For plain bore variants, the bore should be a close sliding fit on the shaft. For keyed variants, also verify that the keyway dimensions (width × depth) match the key already cut on your shaft, or that you can cut a matching key.
A plain bore sprocket has a smooth round hole and relies on a set screw, interference fit, or external clamping to transmit torque. A keyed bore sprocket has a machined slot (keyway) that accepts a rectangular key inserted between the shaft and sprocket, providing a positive mechanical connection that handles higher torque loads and prevents rotational slipping under load.
These sprockets are machined from steel and are suitable for general indoor and sheltered outdoor use. For environments with moisture, chemicals, or salt exposure, periodic lubrication of both the sprocket and chain is recommended to extend service life. If your application requires corrosion resistance, consider applying a protective coating after installation.
Yes. 04C (#25) chain and sprockets are commonly used on small go-karts, mini-bikes, and motorized scooters where compact, lightweight drive systems are needed. Ensure the bore matches your axle or engine output shaft diameter, and select the tooth count that gives your desired top speed and torque balance.
Yes. This listing covers the sprocket only. You will need a compatible 04C / ANSI #25 roller chain sold separately. When replacing a sprocket, it is good practice to also replace the chain if it shows signs of stretch or wear, as a worn chain will accelerate wear on a new sprocket.
