Roller Chain & Sprocket Dimensions

The charts below cover British Standard (BS) roller chain dimensions, ANSI roller chain dimensions, and the sprocket geometry formulas used to work out pitch, root, and outside diameter for a sprocket of any tooth count.

BS ROLLER CHAIN DIMENSIONS

British Standard (BS, to ISO 606) roller chain is identified by a number such as 08B, where the digits give the pitch in sixteenths of an inch and the "B" identifies it as British Standard series. A "-1", "-2" or "-3" suffix identifies simplex (single strand), duplex (double strand), or triplex (triple strand) chain. The reference letters below follow the same physical features as the diagrams further down the page: P is pitch, D2 is roller diameter, D6 is pin diameter, L is the width between sidebars (inner width), and H is sidebar height.

06B-1, 06B-2 and 06B-3 are bush chains (no rollers), so their "D2" value is the bush diameter rather than a true roller diameter. 81-1 and 83-1 are lightweight chains sharing the same 1/2" pitch as the 08B series but with different roller, pin, and sidebar dimensions, so they are not interchangeable with 08B or with each other's sprockets.

ANSI ROLLER CHAIN DIMENSIONS

Roller chain size is identified by its ANSI chain number: the digits to the left of the last digit give the pitch in eighths of an inch (a No. 40 chain has a 4/8", or 1/2", pitch), and the final digit is 0 for a standard chain, 1 for a lightweight chain, or 5 for a chain without rollers.

Chain No. 25 and 35 have no rollers, so their "Dr" value is the bushing diameter rather than a true roller diameter. Dynamic strength values are for standard series chain; heavy series chain (identified by an "H" suffix) uses thicker link plates and is rated separately by the manufacturer.

SPROCKET DIMENSIONS

Unlike chain, a sprocket's size depends on both the chain pitch and how many teeth it has, so rather than a fixed size chart, sprockets are worked out from a small set of formulas. The three key diameters are shown below.

Where P is the chain pitch, Dr is the chain's roller diameter (both from the chain table above), and N is the number of teeth on the sprocket. The outside diameter formula is the standard ASME B29.1 approximation and is accurate enough for most design purposes; manufacturers may hold slightly different values for the exact tooth form.

As a rule of thumb, a drive sprocket is usually specified with 17 teeth or more, and an idler sprocket with 11 or more, to keep chordal action (the slight speeding up and slowing down of the chain as it wraps each tooth) within acceptable limits.