Roller chain sprockets: #25 (6.35 mm) and #35 (9.525 mm), 10–40 T — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/roller-chain-sprockets/  (CC BY 4.0)
Basis: ANSI B29.1 roller chain: #25 pitch 6.35 mm, roller Ø3.30, width 3.18; #35 pitch 9.525, roller Ø5.08, width 4.78; #40 pitch 12.70, roller Ø7.92. PD = pitch / sin(180°/N), OD ≈ pitch × (0.6 + cot(180°/N))
Catalog version: 2026-10-20

Sizes: see table below
- #25 is the small 'bicycle-chain-looking' chain on printers and robots: 6.35 mm (1/4 in) pitch, Ø3.30 rollers, 3.18 mm inner width. #35 is 3/8 in pitch (go-karts, heavier robots). #40 is 1/2 in (bicycles use 1/2 in pitch too but a narrower #410/#415 width).
- Pitch diameter = pitch / sin(180°/N): #25 20 T → 40.6 mm; #35 20 T → 60.9 mm. Centre distance between sprockets must put a whole number of links on the chain: L (links) = 2C/p + (N1 + N2)/2 + (N2 − N1)²p/(4π²C); round to an even number.
- Tooth profile here is the simple roller-seat form (ANSI 'standard' profile approximated): printed PETG #25 sprockets run fine at model speeds; buy steel for anything over 50 W.
- LES: #25 chain from the flywheel to the generator where a belt would slip on a hot shaft; 10 T on the engine, 30 T on the alternator.

chain  teeth  pitch_dia_mm  od_mm  pitch_mm
#25  10  20.55  23.35  6.35
#25  12  24.53  27.51  6.35
#25  15  30.54  33.68  6.35
#25  20  40.59  43.9  6.35
#25  25  50.66  54.08  6.35
#25  30  60.75  64.23  6.35
#25  40  80.93  84.49  6.35
#35  10  30.82  35.03  9.525
#35  12  36.8  41.26  9.525
#35  15  45.81  50.53  9.525
#35  20  60.89  65.85  9.525
#35  30  91.12  96.34  9.525

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Roller chain — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Roller_chain
- McMaster-Carr: Roller chain sprockets (free STEP per part, for your own design use; no redistribution) — STEP, PDF — McMaster-Carr site terms [verify license at link] — https://www.mcmaster.com/products/roller-chain-sprockets/
- Wikipedia: Sprocket — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Sprocket
- Long Earth Society: Engine and rig builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 12 parts): https://xemstudio.com/files/hardware/roller-chain-sprockets/index.json
API: https://xemstudio.com/api/geometry?object=roller-chain-sprockets