Guides / 08B vs ANSI 40: European or American chain
08B vs ANSI 40: European or American chain
Both are sold as “1/2-inch chain”, both have exactly the same pitch, and side by side they look identical. But a sprocket cut for one does not run right with the other. Here is what changes.
Two standards for the same pitch
- ANSI 40 (also #40, RS40, or 08A in ISO) is the American chain, standard ANSI/ASME B29.1. It dominates in North America and on most Asian machinery.
- 08B is the European chain, ISO 606 B series (formerly DIN 8187, also called British Standard). Common on machinery built in Europe.
The pitch is the same, the roller and inner width are not:
| Dimension | ANSI 40 | 08B | Difference |
|---|---|---|---|
| Pitch | 0.500" | 0.500" | 0 |
| Roller diameter | 0.312" (7.92) | 0.335" (8.51) | 0.59 mm |
| Inner width | 0.309" (7.85) | 0.305" (7.75) | 0.10 mm |
| 20T sprocket: pitch dia. | 3.196" | 3.196" | 0 |
| 20T sprocket: bottom dia. | 2.884" | 2.861" | 0.59 mm |
| 20T sprocket: tooth width | 0.287" | 0.284" | 0.09 mm |
Per ANSI B29.1 and ISO 606. Millimeters in brackets.
Can you mix them?
Because the pitch diameter is the same, the chain does go onto the other sprocket, which is why the mix-up is so common. But it does not run well:
- 08B chain on an ANSI 40 sprocket: the roller is 0.59 mm larger than the seat the tooth was cut for. The chain rides high on the flanks instead of the root, pounds, and wears quickly.
- ANSI 40 chain on an 08B sprocket: the roller is loose in the seat. It works under light load, but with play, noise and accelerated wear.
The recommendation is not to mix them. For a temporary repair it may do, but when you replace parts, the sprocket should match the chain standard.
How to tell them apart in a minute
- Measure the roller with a caliper. 0.312" (7.9 mm) is ANSI 40; 0.335" (8.5 mm) is 08B. The 0.6 mm difference is easy to see.
- Read the markings. Most chains have the size stamped on the plates: “40”, “RS40”, “40-1”, “08B-1”.
- On the sprocket, measure root to root. With 20 teeth: 2.884" is ANSI 40 and 2.861" is 08B.
The chain and sprocket identifier runs this comparison automatically from your readings.
The same applies to every pitch
Each pitch has an American and a European version:
| Pitch | ANSI | Roller | ISO B | Roller |
|---|---|---|---|---|
| 3/8" | ANSI 35 | 0.200" | 06B | 0.250" |
| 1/2" | ANSI 40 | 0.312" | 08B | 0.335" |
| 5/8" | ANSI 50 | 0.400" | 10B | 0.400" |
| 3/4" | ANSI 60 | 0.469" | 12B | 0.475" |
| 1" | ANSI 80 | 0.625" | 16B | 0.625" |
| 1 1/4" | ANSI 100 | 0.750" | 20B | 0.750" |
| 1 1/2" | ANSI 120 | 0.875" | 24B | 1.000" |
| 1 3/4" | ANSI 140 | 1.000" | 28B | 1.100" |
| 2" | ANSI 160 | 1.125" | 32B | 1.150" |
| 2 1/2" | ANSI 200 | 1.562" | 40B | 1.550" |
| 3" | ANSI 240 | 1.875" | 48B | 1.900" |
Watch out at 1" (ANSI 80 and 16B): the roller is practically the same (0.625"). The difference is the inner width (0.620" on ANSI 80 vs 0.670" on 16B): measure between the inner plates.
Simplex, duplex and triplex
The number after the dash is the strand count: 40-1 is simplex, 40-2 duplex and 40-3 triplex; in ISO, 08B-1, 08B-2 and 08B-3. The transverse pitch between strands also differs between standards (0.566" on ANSI 40 vs 0.548" on 08B), so a European duplex sprocket won't fit an American duplex chain. The sprocket calculator gives the total tooth width for each case.