Roller Chain Size Table
| Chain number | Pitch | Pitch (inches) | Roller width | Typical use |
|---|---|---|---|---|
| 25 | 2/8 in | 1/4 | 1/8 | Small mechanisms, conveyors |
| 35 | 3/8 in | 3/8 | 3/16 | Small engines, timing drives |
| 41 | 4/8 in | 1/2 | 1/4 | Karts, light duty (thin 40) |
| 40 | 4/8 in | 1/2 | 5/16 | General power transmission |
| 50 | 5/8 in | 5/8 | 3/8 | Heavy machinery, farm drives |
| 60 | 6/8 in | 3/4 | 1/2 | Heavy drives, conveyors |
| 80 | 8/8 in | 1 | 5/8 | Industrial heavy duty |
ANSI roller chain numbers look arbitrary until you see the code: the number is the pitch in eighths of an inch, times ten. Chain 40 runs on a 4/8-inch (half-inch) pitch - forty divided by ten is the numerator over eight. Chain 60 is 6/8 (three-quarter inch), chain 80 a full inch, and the skinny 25 is 2/8 (quarter inch). Every chain that shares a number shares the pitch, and pitch is what makes sprockets interchangeable: a 40 chain runs on any 40 sprocket regardless of maker. The width column then splits the family - 40 is standard width while 41 is the same half-inch pitch on a thinner, lighter chain, which is why 41 shows up on go-karts and small engines where 40 would be overkill.
The chart below carries the everyday ANSI ladder from 25 to 80 with pitch and roller width. The same half-inch pitch hides in a place most people never suspect: single-speed and BMX bicycles run 410-type chain on the 1/2-inch pitch - the bicycle is a chain-40-pitch machine wearing light clothing. That shared pitch is why a chain breaker sized for 40/41/420 works on bike chains, and why sprocket math transfers across the garage. Chain is specified by pitch first (does it fit the sprocket) and width second (how much load it carries), and the number encodes exactly the first half of that decision.
How to use
- Count eight pins and measure end to end, then divide by eight: pins sit on half-pitch centers, so eight pins span four pitches - a chain measuring 2 inches across eight pins is a 40 (four pitches of half inch each).
- Match the number to the sprocket before anything else: pitch must be exact - a 40 chain will not seat on a 50 sprocket or vice versa, and forcing the match shows up as skipped teeth under load.
- Then pick the weight class: where two chains share a pitch (40 versus 41), the wider chain carries more load and the narrower one saves weight and friction - small engines and karts take 41, general drive work takes 40.
Frequently asked questions
What does chain number 40 mean, and what is the code?
The ANSI code packs the pitch into four digits: divide by ten to get eighths of an inch. Chain 40 is 4/8 inch - a half-inch pitch, which is why it is the most common chain in the world: half-inch pitch is the crossover point of small mechanical power. Chain 25 is 2/8 (a quarter inch), 35 is 3/8, 50 is 5/8, 60 is 6/8 (three quarters), and 80 is a full inch. The suffix system extends the code: 40H is heavy duty 40, and the four-digit motorcycle sizes (420, 428, 520 and so on) put pitch in the first digit pair and roller width in the second - 420 is 4/8 pitch with 2/8 rollers, reading on the same eighth-inch grammar. Once the code is visible, a parts bin sorts itself: same first digit pair, same sprockets; bigger second pair, heavier duty.
What is the difference between 40 and 41 chain?
Same pitch, different figure. Both run on 1/2-inch pitch, so either chain meshes with the same sprockets - but 40 is the standard-width chain with full-size rollers for general power transmission, while 41 is the thin version: narrower rollers and thinner link plates, built to carry lighter loads with less weight, less friction and lower cost. The 41 chain is the favorite on go-karts, small conveyors, generators and anything with a few horsepower and no shock loads; 40 owns pumps, shop machinery and farm drives where the extra metal earns its keep. The interchange trap is strength, not fit: a 41 will run happily on 40 sprockets and vice versa, but substituting down because the price is better turns into a stretched chain the first time the load spikes. Match the width to the load and let the shared pitch do the fitting.
Is bicycle chain the same as ANSI 40?
It runs on the same pitch: single-speed and BMX bicycle chain is 1/2-inch pitch, the same spacing as chain 40 and 41 - which is why a standard chain tool handles both bike chains and small-engine chain. But bicycle chain is its own lightweight branch of the family, not a 41: it is narrower still, runs on derailleurs designed to shift across cog clusters (multi-speed chains come in width grades matched to the number of cogs), and carries nothing like the tensile loads of a drive chain. The practical takeaways: pitch-matched tools and measures cross over freely, chain-length math works the same way, but a bicycle chain belongs on a bicycle - its plates and rollers are too slight for engine duty, and a 41 on a derailleur drivetrain will not shift. The shared pitch is a family resemblance, not an interchange ticket.
How do I identify an unmarked chain?
Measure the pitch and the width, then read the code backwards. Pitch first: measure center-to-center over ten pins and divide by ten - 0.375 inch is 35, 0.5 inch means 40 or 41, 0.625 is 50, 0.75 is 60, 1.0 is 80. Then the width: at half-inch pitch, roughly 5/16-inch roller width is standard 40 and the noticeably thinner one is 41; motorcycle sizes 415 and 420 sit between bike and kart territory. A caliper makes this a two-minute job; a ruler over ten pins does it in three. Two cautions from the field: measure over a straight, tensioned section - a worn chain reads long, and the elongation you just measured is itself the wear verdict (half a pitch of stretch over the section means the chain has eaten its sprockets and both should go together); and when in doubt at half-inch pitch, buy by width class and count plates - the sprocket only ever cares about the pitch.