Drive Sprockets Guide: Teeth, Fitment and Replacement

A drive sprocket is the toothed wheel on the final drive that engages the chain's bushings and converts torque into travel. Everything else in the undercarriage is either holding the chain in line or carrying weight; the sprocket is the only part pulling. That is why its tooth profile and its pitch have to match the chain exactly, and why a sprocket that is running out of line wears the belt and itself at the same time - the two failures accelerate each other.

Last updated: October 6, 2026

This page is the entry point for what we publish about sprockets: how a sprocket is identified, what the mounting dimensions have to match, how to read wear, when to replace the sprocket and chain together, and how to buy in Canada. If you already have the part number, the sprocket range is the fastest route.

How a sprocket is identified

Four facts identify a drive sprocket, and they are the same four you should expect a supplier to quote back. The part number, cross-referenced against the machine's model and serial number - Cat's 260-6341 for the 304C CR and 305C CR is a useful example of a number that covers a specific group of machines and not their neighbours. Tooth count, which has to suit the chain's pitch. Bolt count and bolt circle, which is what attaches the sprocket to the final drive. And the bore or pilot diameter with the hub height, because a sprocket can be dimensionally close in every other respect and still not seat or run true.

Nobody can confirm a fitment from a photograph. The reliable method is to hold the old and new sprockets side by side with the old one clean - teeth, bolt holes, pilot diameter and hub depth compared directly - and to treat a difference in any of them as a stop. Where the machine has been through a generation change, that check is the only one that matters, which is the same reasoning used on the 304C CR and 305C CR sprocket.

When a sprocket is worn out

A sprocket wears into a hook. Look at the tooth from the side: a new sprocket's tooth has a flat, square drive face, and as it runs that face curves forward until the tooth looks like a hook. Once the hook has formed, the chain no longer seats properly, it climbs the teeth under load, the pitch stretches, and both parts wear faster together.

Four observations cover the diagnosis. Hooked or sharpened teeth mean the sprocket is finished. Wear concentrated on one side of the teeth means the chain is running out of line, and a replacement will wear the same way. Chipped or cracked teeth point at impact or a foreign object in the chain, and the chain should be inspected link by link. A shiny, polished tooth face with little hook is normal running-in, not a reason to replace anything. The symptoms the operator notices first are noise, a chain that will not hold pitch, and a machine that climbs out of the chain when it pushes into a pile.

How those signs are read in practice is covered by how to check a sprocket's wear indicator, and what the teeth have to be for the chain to last is behind how compatible a sprocket is with different chains.

Sprocket and chain as a pair

The single most expensive mistake with a drive sprocket is fitting a new one under a stretched chain, or the reverse. A chain that has elongated no longer matches the sprocket's tooth spacing, so it climbs the teeth and wears the new sprocket into a hook quickly; a new chain on a hooked sprocket wears its bushings from the inside out. Where both are worn, they are replaced as a pair, and the cost of doing so once is almost always less than the cost of a premature second repair.

Alignment matters just as much as wear. If the chain rides up one side of the teeth through a full rotation, the final drive or the track frame is not running true - a different repair from a new sprocket, and one that a replacement will not fix. That is why the inspection should include watching the chain seat as the machine is driven slowly forward and back.

Buying a sprocket in Canada

Four items belong in writing: the part-number cross-reference for your model and serial number; the specification as supplied, including tooth count, bolt count and mounting dimensions; the warranty terms as a period plus an operating-hours cap, whichever comes first, with freight responsibility named; and the stock position with a delivery date. On a machine that is down, the delivery date usually decides the purchase.

Two habits make the next replacement cheaper. Keep the old sprocket's dimensions on file, because on a machine that has been through a generation change or a rebuild that record is what confirms the number the second time. And price the job rather than the part: if the chain is due as well, a pair quoted together is normally less than two orders placed a month apart, which is the same argument made in how aftermarket sprockets compare to OEM on the PC300.

Bolt-on, hub and split sprockets

Sprockets arrive in three practical forms, and which one a machine uses decides how much of the final drive has to come apart. A bolt-on sprocket attaches to the final drive flange with a ring of bolts, which is the usual arrangement on compact excavators and track loaders: unbolt the old one, seat the new one, torque it, and the job is done at the track end of the machine. A hub sprocket is integral with, or pressed onto, a hub that carries the final drive's bearings, so replacing it involves more of the drive. And a split sprocket is made in segments so it can be changed without breaking the chain - the slowest to buy and the fastest to fit, which is why it is used where downtime costs more than the part.

Which one a machine takes is fixed by its design, but it changes what "replacing a sprocket" means in hours. It is worth establishing that before ordering, because a bolt-on replacement priced against a hub job is not a comparison at all.

Measuring wear rather than judging it

The wear indicator on a sprocket is the profile of the tooth where the bushing drives. Two measurements make the decision objective. The first is the tooth's drive-face profile: on a new sprocket the face is flat and square, and as it wears the face curves forward into the hook shape. The second is the sprocket's pitch diameter - the effective circle the chain runs on - because a sprocket can look acceptable from above while its teeth have worn enough to change that diameter.

Compare the measured profile against the machine's specification rather than against an impression. A sprocket that is uniformly polished with a square face is running in, not wearing out, and replacing it early simply puts a new part through the same bedding-in process. A sprocket with one side worn harder is the one to look at closely, because that pattern points at an alignment problem that will follow the replacement.

The rest of this cluster

Choosing one: heavy-duty sprockets for mining, precision-engineered sprockets for undercarriage and choosing a Komatsu bulldozer sprocket. How they are specified: tooth count, wheel diameter, pitch and type for the application. Replacing one: replacing the sprocket on a Cat D7 dozer. Buying online: sprockets for Caterpillar excavators in Canada and buying a Komatsu PC200 sprocket online. Related parts: what an idler sprocket is, driven sprockets and the 260-6341 sprocket in Canada. Wider picture: excavator undercarriage parts.

FAQs

How do I know which drive sprocket fits my machine?

By the part number cross-referenced against your model and serial number, then confirmed against tooth count, bolt count, bolt circle, bore and hub height - best done by comparing the old and new sprockets side by side.

When should a sprocket be replaced?

When the teeth are hooked or sharpened, when one side wears faster than the other, when teeth are chipped or cracked, or when the chain starts climbing out of the sprocket under load.

Should the sprocket and chain be replaced together?

Where both are worn, yes. A new sprocket under a stretched chain wears quickly, and a new chain on a hooked sprocket wears its bushings out - doing them as a pair is usually cheaper than two repairs.

Does tooth count have to match exactly?

Yes. Tooth count and pitch together determine how the chain seats, and a sprocket that is close but wrong will wear the chain and itself. It is not a dimension to approximate.

Are aftermarket sprockets suitable for excavators?

When they are documented: a part-number cross-reference, tooth and bolt counts, mounting dimensions, and warranty terms with an hours cap. Undocumented, the photograph is the whole product.