Roller chain and sprocket guide: chain size chart, tooth count, link count and centre distance

Reading chain numbers: pitch and size chart

ANSI and JIS roller chains are numbered: all digits but the last × 1/8 inch give the pitch — No.40 = 4/8" = 12.7 mm, No.60 = 6/8" = 19.05 mm. A final 0 means standard roller chain, 1 a lightweight chain (No.41), 5 a rollerless bushing chain (No.25, No.35). ISO 606 writes 08A: the first two digits × 1/16" are the pitch, A marks the ANSI-derived series.

Nominal single-strand dimensions. The minimum tensile strength is the ISO 606 breaking limit, not a working load: size chains from the manufacturer's power-rating tables for your power and small-sprocket speed. Working tension is typically 1/7–1/10 of breaking strength or less.

TIP08A (No.40) and 08B (British-standard chain) share a 12.7 mm pitch, but roller diameter (7.92 vs 8.51 mm) and inner width differ, so sprocket tooth forms are not interchangeable. Check A or B series before buying.

Sprocket tooth count and chordal action

Chain wraps a sprocket as a z-sided polygon, not a circle. At constant sprocket speed the chain's linear speed cycles between radius R and R·cos(180°/z) — chordal action — causing speed variation, vibration and noise, worse with fewer teeth.

Pitch diameter dp = p / sin(180°/z)　　Speed variation = 1 − cos(180°/z)

• Use ≥ 17 teeth on the small sprocket; ≥ 21 for high speed or shock loads.
• Keep the ratio ≤ 7:1 and the small-sprocket wrap ≥ 120°.
• An odd tooth count with an even link count makes each roller meet different teeth in turn, spreading wear.
• Don't overdo large sprockets: worn chain rides up the teeth, and a rule of thumb limits allowable elongation to about 200 / z₂ % (max ≈ 3%), so big sprockets skip sooner.

Link count and centre distance

Lp = 2C/p + (z₁ + z₂)/2 + ((z₂ − z₁) / 2π)² · p / C

Lp is the number of links, C the centre distance, p the pitch. Round Lp to an integer — preferably even. Roller chain alternates inner and outer links, so an even count closes with a standard connecting link; an odd count needs an offset (half) link, which is weaker and best avoided under high load.

C = p/4 · [ (Lp − (z₁+z₂)/2) + √( (Lp − (z₁+z₂)/2)² − 8·((z₂ − z₁)/2π)² ) ]

Example: No.40, 17 and 34 teeth, target 300 mm. Lp = 47.24 + 25.5 + 0.31 = 73.05 → round to 74 links, giving an actual C ≈ 306.0 mm and a chain length of 74 × 12.7 = 939.8 mm. Centre distance is typically 30–50 pitches (380–635 mm for No.40), at most about 80.

TIPThe chain centre distance calculator rounds to an even link count, returns the actual centre distance and wrap angle, and links straight to both sprockets.

Chain speed, lubrication and tension

Chain speed v = z · p · n / 60000 (m/s)

No.40, 17 teeth at 300 rpm: v = 17 × 12.7 × 300 / 60000 ≈ 1.08 m/s. Speed and power decide the lubrication method; manufacturers' rating charts show the ranges:

• Manual or drip: slow, light drives — oil the plate gaps regularly.
• Oil bath or slinger disc: medium speed, with the lower strand dipping in oil.
• Forced (pump) lubrication: high speed and load, spraying the inside of the chain.
• Where oil isn't allowed (food, clean rooms), use self-lubricating or stainless chain, at a lower rating.

Leave sag on the slack side — about 2–4% of the centre distance for horizontal drives, per the manufacturer. Too tight accelerates wear and bearing load; too slack causes skipping and whipping. If the centre distance is fixed, add an idler on the slack side. Replace chain at about 1.5% elongation and inspect the sprocket teeth at the same time.

3D-printed and CNC sprockets

• Slow, light robot or bicycle prototypes can use PETG, nylon or PA-CF sprockets; heavy or continuous duty still calls for steel or CNC parts.
• Print sprockets flat for the best tooth form; add 0.1–0.2 mm to the bore and use a keyway or D-bore to stop slipping.
• Tooth width follows the JIS single-strand table, slightly narrower than the chain's inner width; the ISO side chamfer guides the chain on.
• The hub must stay inside the chain's inner-plate clearance diameter or the plates will rub it.

The sprocket generator models the ISO 606 / JIS B 1801 tooth form for No.25–80, types A / B / C and keyway bores. Download the STEP and send it to Orinovate for a CNC or 3D-printing quote.