ANSI #40 and ISO 08B Are Both 1/2 Inch Pitch - And They Do Not Interchange
Transmission chain and matched sprockets
Target keyword: ANSI vs ISO roller chain
Secondary: 08B vs 40 chain, DIN 8187 roller chain, roller chain size chart
Meta description: ANSI #40 and ISO 08B share a 12.70 mm pitch but differ in roller diameter and inner width. Full dimension tables for both standards and why substitution destroys sprockets.
A buyer orders "half-inch pitch chain." The supplier ships 08B. The machine was built around #40 sprockets. Everything measures 12.70 mm pitch, so it goes on.
Three weeks later the sprocket teeth are worn into hooks and the chain is jumping.
Both chains are genuinely 12.70 mm pitch. Both fit on the shaft. And they are not interchangeable, because pitch is only one of four dimensions that have to match.
The two standards
ANSI / ASME B29.1 is the American standard, sizes designated by number: #25, #35, #40, #50, #60, #80 and up. The number is the pitch in eighths of an inch - #40 is 4/8", #80 is 8/8".
ISO 606 / DIN 8187 is the European B-series, designated 04B, 05B, 06B, 08B, 10B, 12B, 16B, 20B, 24B. Here the number is pitch in sixteenths of an inch - 08B is 8/16" = 1/2".
Both arrive at 1/2 inch. They get there with different internal proportions.
ANSI B29.1 dimensions
From the ASME B29.1-2011 standard dimensions:
|
Chain |
Pitch |
Max roller Ø |
Inner width |
Pin Ø |
Plate thickness |
Min tensile |
|
#25 |
6.35 mm |
3.30 mm* |
3.18 mm |
2.30 mm |
0.76 mm |
780 lb (3.5 kN) |
|
#35 |
9.53 mm |
5.08 mm* |
4.78 mm |
3.58 mm |
1.27 mm |
1,760 lb (7.8 kN) |
|
#40 |
12.70 mm |
7.92 mm |
7.92 mm |
3.96 mm |
1.52 mm |
3,125 lb (13.9 kN) |
|
#41 |
12.70 mm |
7.77 mm |
6.35 mm |
3.58 mm |
1.27 mm |
1,500 lb (6.7 kN) |
|
#50 |
15.88 mm |
10.16 mm |
9.53 mm |
5.08 mm |
2.03 mm |
4,880 lb (21.7 kN) |
|
#60 |
19.05 mm |
11.91 mm |
12.70 mm |
5.94 mm |
2.39 mm |
7,030 lb (31.3 kN) |
|
#80 |
25.40 mm |
15.88 mm |
15.88 mm |
7.92 mm |
3.18 mm |
12,500 lb (55.6 kN) |
|
#100 |
31.75 mm |
19.05 mm |
19.05 mm |
9.53 mm |
3.96 mm |
19,530 lb (86.9 kN) |
|
#120 |
38.10 mm |
22.23 mm |
25.40 mm |
11.10 mm |
4.75 mm |
28,125 lb (125.1 kN) |
|
#140 |
44.45 mm |
25.40 mm |
25.40 mm |
12.70 mm |
5.56 mm |
38,280 lb (170.3 kN) |
|
#160 |
50.80 mm |
28.58 mm |
31.75 mm |
14.27 mm |
6.35 mm |
50,000 lb (222.4 kN) |
|
#200 |
63.50 mm |
39.67 mm |
38.10 mm |
19.84 mm |
7.92 mm |
78,125 lb (347.5 kN) |
\#25 and #35 have no rollers - the figure is bushing diameter.
Note #41 sitting alongside #40. Same pitch, narrower, lighter, roughly half the strength. It is a light-duty chain and it is not a substitute for #40, though the pitch match tempts people into trying.
ISO 606 / DIN 8187 B-series
British Standard dimensions, conforming to ISO 606 and DIN 8187:
Figure 1. ANSI #40 against ISO 08B. Only pitch matches.
|
Chain |
Pitch |
Inside width b min |
Roller Ø d1 max |
Pin Ø d2 max |
Plate depth |
Tensile |
|
04B |
6 mm |
2.80 mm |
4.00 mm |
1.85 mm |
5.0 mm |
3,000 N |
|
05B-1 |
8 mm |
3.00 mm |
5.00 mm |
2.31 mm |
7.1 mm |
4,600 N |
|
06B-1 |
3/8" |
5.72 mm |
6.35 mm |
3.28 mm |
8.3 mm |
9,100 N |
|
08B-1 |
1/2" |
7.75 mm |
8.51 mm |
4.45 mm |
11.8 mm |
18,200 N |
|
10B-1 |
5/8" |
9.65 mm |
10.16 mm |
5.08 mm |
14.7 mm |
22,700 N |
|
12B-1 |
3/4" |
11.68 mm |
12.07 mm |
5.72 mm |
16.1 mm |
29,000 N |
|
16B-1 |
1" |
17.02 mm |
15.88 mm |
8.28 mm |
21.1 mm |
64,000 N |
|
20B-1 |
1 1/4" |
19.56 mm |
19.05 mm |
10.19 mm |
26.3 mm |
98,000 N |
|
24B-1 |
1 1/2" |
25.40 mm |
25.40 mm |
14.63 mm |
33.3 mm |
170,000 N |
|
28B-1 |
1 3/4" |
30.99 mm |
27.94 mm |
15.90 mm |
37.0 mm |
200,000 N |
The direct comparison
Putting #40 and 08B side by side, using metric figures from a single source for both so the measurement convention matches:
|
Dimension |
ANSI #40 |
ISO 08B |
Difference |
|
Pitch |
12.70 mm |
12.70 mm |
Identical |
|
Roller diameter |
7.95 mm |
8.51 mm |
08B larger by 0.56 mm |
|
Inside width |
7.85 mm |
7.75 mm |
08B narrower by 0.10 mm |
|
Pin diameter |
3.96 mm |
4.45 mm |
08B larger by 0.49 mm |
|
Plate depth |
11.8 mm |
11.8 mm |
Same |
|
Tensile strength |
14,800 N |
18,200 N |
08B stronger by 23% |
Four dimensions. One matches.
The roller diameter difference is the one that wrecks sprockets. A sprocket tooth pocket is cut to seat a specific roller diameter. Put an 8.51 mm roller into a pocket profiled for 7.95 mm and the roller rides high on the tooth flank instead of seating in the root. Contact area collapses to a line, contact stress multiplies, and the tooth wears into a hooked profile within weeks.
The inside width difference works the other way - 08B is 0.10 mm narrower, so the chain fits over a #40 sprocket with slightly less clearance than intended, which matters for alignment tolerance and lubricant access.
The A-series confusion
There is a third family that makes this worse: ISO 606 also defines an A-series - 08A, 10A, 12A, 16A - which does correspond to the ANSI sizes. 08A matches #40, 10A matches #50, 12A matches #60, 16A matches #80.
So in ISO nomenclature:
08A = ANSI #40 dimensions
08B = British/European 1/2" chain, different dimensions
One letter. Completely different chain. If a supplier quotes "08 chain" without the letter, ask.
Why 08B is stronger
Look again: 18,200 N versus 14,800 N, in the same pitch. The B-series achieves that with a larger pin diameter (4.45 vs 3.96 mm) and larger roller.
Figure 2. ANSI B29.1 minimum ultimate tensile strength by size.
That is not a free gain. Larger pins mean more material in the wear interface and a higher-capacity joint, but B-series chain of the same pitch is heavier and has different articulation characteristics. The two standards represent different engineering compromises from different industrial traditions, not better and worse versions of the same thing.
Multi-strand: transverse pitch matters too
For duplex and triplex, the strand spacing (transverse pitch, e) is its own dimension. ANSI figures:
Duplex sprocket, cut for the correct transverse pitch
|
ANSI |
Transverse pitch e |
Duplex tensile |
Triplex tensile |
|
25 |
6.40 mm |
6,800 N |
10,200 N |
|
35 |
10.13 mm |
16,800 N |
25,200 N |
|
40 |
14.38 mm |
29,600 N |
44,500 N |
|
50 |
18.11 mm |
48,800 N |
73,300 N |
|
60 |
22.78 mm |
68,000 N |
102,100 N |
|
80 |
29.29 mm |
129,000 N |
193,600 N |
|
100 |
35.76 mm |
200,000 N |
300,000 N |
|
120 |
45.44 mm |
260,000 N |
390,000 N |
|
160 |
58.55 mm |
454,000 N |
681,000 N |
|
200 |
71.55 mm |
720,000 N |
1,080,000 N |
Two useful observations.
Duplex tensile is exactly 2× simplex and triplex is exactly 3× in these published figures. In practice, load sharing between strands is never perfect - misalignment and manufacturing variation mean one strand carries more. Do not design to the full multiple without margin.
And a duplex sprocket must match both the chain size and the transverse pitch. A #40 duplex sprocket is cut for 14.38 mm strand spacing; an 08B duplex sprocket is cut for its own value. Another way the two standards fail to interchange.
Minimum tensile is not a working load
The tensile figures above are minimum ultimate tensile strength - the load at which the chain breaks in a single pull. They are not operating loads.
A useful relationship from the published ANSI data: standard-series minimums follow roughly 12,500 × pitch² (pitch in inches). Check it - #40: 12,500 × 0.25 = 3,125 lb. #80: 12,500 × 1.0 = 12,500 lb. #160: 12,500 × 4.0 = 50,000 lb. The formula holds across the series.
Two reasons never to size on UTS:
Fatigue. Chain operating at a fraction of ultimate strength still fails by plate fatigue after enough cycles. Fatigue limit is far below ultimate.
Dynamic loading. Chordal action, shock loads, and acceleration all add to the steady tension. Published data also shows typical average tensile running well above the minimum - #40 at around 4,188 lb average against a 3,125 lb minimum - which tempts people to design closer to the limit. Design to the minimum, not the average.
Identifying unmarked chain
When a machine arrives with chain and no documentation:
Measure pitch over 10 or 12 links and divide - more accurate than one link, and it also reveals wear elongation.
Measure roller diameter with calipers. This is the discriminator: at 1/2" pitch, 7.92–7.95 mm means ANSI #40, 8.51 mm means 08B.
Measure inner width between plates.
Measure pin diameter where visible.
Roller diameter alone resolves most cases, because that is where the two standards diverge most and it is easy to measure.
FAQ
Can I run 08B chain on #40 sprockets in an emergency?
It will turn. The rollers will not seat properly, sprocket wear will accelerate sharply, and you will be replacing the sprockets rather than just the chain. Acceptable as a stopgap for hours, not weeks.
Which is stronger, #40 or 08B?
08B - 18,200 N against 14,800 N, from the larger pin and roller.
What is 08A?
The ISO A-series equivalent of ANSI #40. Same dimensions as #40. Not the same as 08B.
Why do #25 and #35 have no rollers?
They are bushing chains. At those small pitches a separate roller is impractical, so the chain articulates on the bushing directly. This is why their "roller diameter" figure is bushing OD.
Is #41 a cheaper #40?
No - it is a lighter-duty chain with narrower plates and roughly half the tensile strength. Same pitch, different application class.
Are duplex chains twice as strong as simplex?
The published ratings say exactly 2×, but real load sharing between strands depends on alignment and manufacturing tolerance. Keep margin.
Tianjin OuNaiDa Transmissions Technology manufactures transmission chain and matched sprockets to both ANSI B29.1 and ISO 606 / DIN 8187. If you are unsure which standard your machine uses, send us the roller diameter and inner width and we will identify it.
