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When a worn or mismatched sprocket is causing chain skip, premature wear, or unexpected downtime, finding an exact-fit replacement matters. This 08B-1 roller chain sprocket is designed for engineers, machine builders, and serious DIYers who need a dimensionally accurate, drop-in solution for ISO/BS 08B-1 standard chain drives.
Each sprocket is machined from C45 medium-carbon steel and finished with a black oxide coating for corrosion resistance. The tooth profile conforms to the 08B-1 standard with a 1/2" (12.7mm) pitch. Bore sizes range from 10mm to 40mm with matching keyways (4mm, 5mm, 6mm, 8mm, 10mm, or 12mm depending on bore), and tooth counts span 10 to 20 teeth to suit a wide range of speed ratios.
Typical applications include conveyor drive systems requiring precise chain engagement, agricultural machinery gearbox output shafts, and light industrial automation equipment where an 08B-1 roller chain sprocket with a keyed bore provides reliable torque transmission without slippage.
Machined from C45 medium-carbon steel for a balance of machinability, tensile strength (typically 570–700 MPa), and wear resistance under cyclic chain loading.
The black oxide surface treatment provides a base level of corrosion resistance and reduces light reflection — suitable for indoor and sheltered outdoor drive applications.
Each bore is machined with a matching keyway (4mm, 5mm, 6mm, 8mm, 10mm, or 12mm) to ensure positive torque transmission and prevent rotational slippage on the shaft.
Tooth geometry conforms to the 08B-1 standard (1/2" pitch, 7.94mm roller diameter), ensuring smooth engagement and minimal chain wear across the full tooth count range of 10–20T.
Order a single sprocket for a direct replacement, or select the 2-piece option to replace both drive and driven sprockets simultaneously and maintain a matched wear pair.
With 11 tooth counts (10–20T) and up to 17 bore sizes (10–40mm), this range covers the majority of 08B-1 drive configurations without requiring custom machining.
| Chain Standard | ISO/BS 08B-1 |
|---|---|
| Chain Pitch | 1/2" (12.7 mm) |
| Roller Diameter | 7.94 mm (5/16") |
| Number of Teeth | 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20 |
| Bore Size Range | 10 mm – 40 mm (with keyway) |
| Keyway Width | 4 mm (≤12mm bore) / 5 mm (14–17mm) / 6 mm (18–22mm) / 8 mm (24–30mm) / 10 mm (32–35mm) / 12 mm (40mm) |
| Material | C45 Medium-Carbon Steel |
| Surface Finish | Black Oxide |
| Hub Style | See variant options |
| Outside Diameter | See variant options |
| Hub Diameter | See variant options |
| Weight | See variant options |
The tooth count determines your drive ratio. Divide the driven sprocket teeth by the drive sprocket teeth to get the reduction ratio. For example, a 10T drive and 20T driven sprocket gives a 2:1 reduction. As a general rule, using at least 17 teeth on the drive sprocket reduces chain wear and noise — smaller tooth counts are acceptable for low-speed or space-constrained applications.
Use a digital caliper to measure the shaft diameter at the mounting location. Select the bore size that matches your shaft exactly — the bore is machined to a standard tolerance and is designed to be used with a key and keyway for a secure fit. Do not select an oversized bore and expect to shim it; this will cause runout and premature wear.
C45 steel (equivalent to AISI 1045) has a typical tensile strength of 570–700 MPa in the normalized condition. It is suitable for moderate-load conveyor drives, agricultural equipment, and general industrial machinery. For high-shock or very high-torque applications, consider whether a hardened or alloy steel sprocket is more appropriate for your load cycle.
Black oxide provides a thin conversion coating that offers mild corrosion resistance — it is not equivalent to zinc plating or stainless steel. For outdoor or humid environments, apply a light machine oil or chain lubricant to the sprocket surface after installation. For fully exposed outdoor use, consider whether a stainless or zinc-plated sprocket better suits your conditions.
This sprocket is designed for ISO/BS 08B-1 roller chain with a 1/2" (12.7mm) pitch and 7.94mm roller diameter. Do not use it with ANSI #40 chain — while both have a 1/2" pitch, the roller diameter and inner link width differ, which will cause poor engagement and accelerated wear. Always match the sprocket standard to your chain standard.
Yes, in most cases. When one sprocket shows significant wear, the mating sprocket and chain have typically worn together as a matched set. Installing a new sprocket against a worn chain (or vice versa) accelerates wear on the new component. The 2-piece option on this listing allows you to replace both drive and driven sprockets simultaneously for the best service life.
C45 steel is machinable, and the bore can be enlarged by a qualified machinist if needed — provided the wall thickness between the bore and the root circle remains sufficient for your load. However, we recommend selecting the closest standard bore size from the available options to avoid the need for secondary machining and to maintain dimensional accuracy.
