Parts of a Chain – Plates, Pins, Rollers and Bushings

All 9 parts on the diagram

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Start here: 5 main parts 5

Outer plate Joined in pairs by two pins to make an outer link. Also called a pin link plate.
Inner plate Joined in pairs by two bushings to make an inner link. Also called a roller link plate.
Pin It holds a pair of outer plates together. It passes through the bushing of the inner link, so the chain can bend.
Roller It turns on the bushing and rolls against the sprocket teeth. That cuts friction and wear.
Link An oval ring that passes through the rings either side of it. A link of a plain link chain.

Roller chain: 6 2

Pitch The pitch: the distance from one pin to the next. Chain sizes are named by it, and a worn chain’s pitch grows.
Bushing It holds the inner plates together. Also called a sleeve. The pin turns inside it and the roller turns outside it.

Joining the chain: 2 2

Connecting link An outer link whose plate slides off. It lets the chain be joined or split with simple tools. Also called the master link.
Spring clip A U-shaped clip that holds the connecting link’s plate on its pins. Also called the horseshoe clip.

How this list was compiled: Read 2026-09-27. (1) Wikipedia, Roller chain, https://en.wikipedia.org/wiki/Roller_chain : inner links have two inner plates joined by two sleeves or bushings on which two rollers rotate; outer links have two outer plates joined by pins that pass through the inner links' bushings; the rollers give rolling contact with the sprocket teeth, cutting wear; the pitch is the spacing of the links, and ANSI sizes give it in eighths of an inch; wear lengthens the pitch; a master or connecting link has a pin held by a horseshoe clip so it can be removed with simple tools; a bicycle chain is a roller chain. (2) Tsubakimoto Chain Co., The Complete Guide to Chain, 1.1.1 and 1.1.4, http://chain-guide.com/basics/1-1-1-structure-power-transmission-chain.html and http://chain-guide.com/basics/1-1-4-functions-of-chain-parts.html : plate, pin, bushing and roller and what each bears; the connecting link, slip fit for assembly; the offset link; cotter pins and spring clips hold the outer plate on at the connection. Licence: own work

The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work

How it works

These are the parts of a chain on a roller chain, the kind on a bicycle: side-on, then from above with one roller cut open, then its connecting link. A plain link chain comes last. Start with the 5 main parts.

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Two kinds of link

A roller chain alternates two links. An inner link is two inner plates joined by bushings, with a roller turning on each bushing. An outer link is two outer plates joined by pins that pass through the next bushings. The distance from pin to pin is the pitch.

Closing the loop

A connecting link, or master link, has a plate that slides off its pins, held by a spring clip, so the chain can be joined or split without special tools.

A bike chain is a roller chain. As its pins and bushings wear, the pitch grows, which is why old chains seem to stretch.

Questions and answers

What is the pitch of a chain?

The distance from the centre of one pin to the next. Chain sizes are named by their pitch; a common bicycle chain has a half-inch pitch.

What does the roller do on a chain?

It turns on the bushing and rolls against the sprocket teeth instead of sliding, so the chain and sprocket wear far less.

What is a master link?

Another name for the connecting link: the one link whose plate comes off, held by a spring clip, so the chain can be opened and closed.