Three measurements identify almost any chain
A chain with no markings isn't a mystery. It is three measurements. Take them with a vernier (a steel rule will do at a pinch), ideally on a cleaned, unworn section:
- Pitch: pin centre to pin centre. On a worn chain, measure over 10 pitches and divide by 10 to average out the wear.
- Roller diameter: the outside of the roller (the part the sprocket tooth touches).
- Inner width: the gap between the inner plates, where the sprocket tooth sits.
Then count the strands (simplex, duplex, triplex) and note anything on the side plates. Most quality chain has the size stamped on the plates, which shortcuts everything.
Chain identifier
Enter what you can measure. Any one of the three is enough to start, and each extra measurement narrows it down. Averaging pitch over 10 pitches? Divide by 10 first.
Crack the ANSI code: the eighth-inch rule
American Standard numbering is a code, not a catalogue quirk. The leading digit(s) are the pitch in eighths of an inch: 40 = 4/8″ (12.70 mm), 50 = 5/8″ (15.875 mm), 60 = 6/8″ (19.05 mm), 80 = 8/8″ = 1″ (25.40 mm). The last digit tells you the type: 0 for standard roller chain, 5 for rollerless bush chain, 1 for light duty (41). A suffix adds the variant: H for heavy series, SS for stainless steel, HP for hollow pin.
British Standard sizes carry a B: 06B (3/8″), 08B (1/2″), 10B (5/8″), 12B (3/4″), 16B (1″). Same pitches, different proportions.
Same pitch, different chain: the roller settles it
The classic identification trap: BS and ANSI chains share pitches, and fitting the wrong one wrecks sprockets. The roller diameter is the tell:
| Pitch | British Standard | Roller Ø | American Standard | Roller Ø |
|---|---|---|---|---|
| 12.70 mm (1/2″) | 08B | 8.51 mm | 40 | 7.92 mm |
| 15.875 mm (5/8″) | 10B | 10.16 mm | 50 | 10.16 mm |
| 19.05 mm (3/4″) | 12B | 12.07 mm | 60 | 11.91 mm |
| 25.40 mm (1″) | 16B | 15.88 mm | 80 | 15.88 mm |
Where the rollers match (10B/50, 16B/80), the inner width and plate dimensions separate them, because BS chain generally runs different plate proportions. If your measurements land between two sizes, the chain is probably worn: go back to the 10-pitch average, or read our guide to measuring chain wear first.
Double-pitch conveyor chain looks like roller chain with gaps. If the pitch measures twice a standard size (25.4 mm with small rollers, say), you're looking at C2040-series double-pitch chain, and if the rollers are fatter than the plates, it's the large-roller (C20x2) type.
Or skip all of it
The shortcut: photograph the chain next to a rule, side-on and top-down, and send it over with any plate markings. We identify chains every day, including obsolete sizes, metric oddities and specials, and we'll match it from UK stock or build it if nobody stocks it any more.
Common questions
What three measurements identify a roller chain?
Pitch (pin centre to pin centre), roller diameter, and inner width between the plates. With those three, almost any standard chain can be identified, or simply send us a photo with the measurements.
How does the ANSI chain numbering work?
The first digit(s) give the pitch in eighths of an inch: ANSI 40 is 4/8 inch (12.7 mm), 60 is 6/8 inch (19.05 mm), 80 is 1 inch. A trailing 0 means standard roller chain; 5 is rollerless; 1 is light duty.
My chain is 12.7 mm pitch. Is it 08B or ANSI 40?
Same pitch, different rollers: 08B has an 8.51 mm roller, ANSI 40 has 7.92 mm. Measure the roller, and if it is still unclear, the plate markings or a photo will settle it.
Got a mystery chain?Send a photo and the three measurements and we'll identify it and quote the replacement.
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