Roller Chain Sizes & Numbering

What it is

Standard power-transmission roller chain in North America is sized by an ANSI chain number defined in ASME B29.1. The number encodes the pitch (the distance between pin centers) and the chain type. Sprockets are sized to the same number, so chain and sprocket must match. Internationally, ISO 606 covers both the ANSI-derived A series and the British-derived B series, which look similar but do not interchange.

How to identify

• Digits before the last digit = pitch in eighths of an inch. 40 → 4/8 = 1/2 in. 80 → 8/8 = 1 in. 100 → 10/8 = 1-1/4 in.
• Last digit = type. 0 = standard roller chain. 1 = lightweight narrow chain (41). 5 = rollerless bushing chain (25, 35).
• Suffix H = heavy series with thicker side plates (e.g. 80H). It uses the same sprockets as the standard chain.
• Dash number = strand count. 60-2 is double-strand 60; 60-1 or plain 60 is single strand.
• ISO codes use sixteenths of an inch for pitch: 08A = 1/2 in pitch A series (same as ANSI 40); 08B = 1/2 in pitch British series (not the same as 40).

To identify an unmarked chain, measure across several pitches pin-center to pin-center and divide, then check roller diameter and inside width — this separates 40 from 41 and 08B.

ANSI chain number and pitch

Key points

• Pitch alone is not enough: 40 and 41 share a pitch but differ in width and roller size, and 08B differs from 40 in roller diameter and width.
• Connecting links and offset links must match the chain number and strand count. Offset links reduce chain strength; avoid them in high-load drives where possible.
• Variants — O-ring, stainless, nickel-plated, self-lubricating, attachment and double-pitch chains — have their own ratings and sprocket requirements. See the chain-type sheets.
• Replace badly worn sprockets with the chain; a new chain on hooked teeth wears out quickly.
• Drive chain is not lifting chain. Never use roller chain for overhead lifting or rigging.

Common mistakes

• Reading 41 as "a kind of 40" and mixing parts.
• Replacing British-standard (B-series) chain on imported equipment with ANSI chain of the same pitch.
• Ordering by length in feet without stating the chain number, strand count and whether a connecting link is needed.
• Using catalog working loads from one brand to approve another brand's chain.

Governing standards: ASME B29.1 (precision power transmission roller chains, attachments and sprockets); ISO 606 (short-pitch transmission precision roller and bush chains). Chain maker's catalog for strengths and ratings.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.