The friction disc, the pressure plate and the release bearing as a minimum, plus an alignment tool - and on many vehicles the concentric slave cylinder as well.

The three core components are the ones that wear together and cannot be reached separately.

The alignment tool centres the disc on the flywheel so the gearbox input shaft will enter. Without it, the gearbox will not go back on.

Four-piece kits add the concentric slave cylinder, which lives inside the bellhousing on many modern vehicles.

Some kits include flywheel bolts, which are usually single-use torque-to-yield fasteners.

What is generally not included is the spigot bearing, the release fork, or a flywheel unless specifically stated - all worth ordering alongside.

By vehicle, engine code and gearbox code together - the same model is routinely offered with more than one clutch.

Disc diameter and the number and size of the input shaft splines are the primary identifiers, and they change with engine output.

The pressure plate's bolt pattern and diaphragm design must match the flywheel and the release mechanism.

Release type is the trap: a vehicle with a concentric slave takes a different kit from one with a fork and an external slave, even with the same engine.

Self-adjusting pressure plates and conventional ones are not interchangeable, and fitting the wrong one gives an unworkable pedal.

Where the vehicle history is unknown, measure the old disc and count the splines before ordering the replacement - it is quicker than a second attempt.

A pressure plate with a mechanism that compensates for disc wear, keeping pedal effort and the bite point roughly constant through its life.

A conventional diaphragm spring gets progressively harder to release as the disc wears, and the bite point rises.

A self-adjusting unit uses a ramp or wedge mechanism to take up wear, so the pedal feels the same at the end of the clutch's life as at the start.

The benefit is a lighter pedal, particularly on heavier commercial applications where conventional pedal effort would be tiring.

The mechanism must be reset or locked before fitting, and every manufacturer has its own procedure and often a special tool.

Fitting one without resetting it is a common error that gives a clutch which will not release properly from new.

Where it is at or near its limit, yes - it is usually cheaper as part of the kit and guarantees the components are matched.

A solid flywheel that is scored, heat-cracked or below its minimum thickness must be machined or replaced, and machining changes the clutch geometry.

A dual-mass flywheel is measured for free play and lateral movement against published figures, and at the age most clutches are changed, many are out of limit.

Kits supplied with a matched flywheel remove the compatibility question entirely, which matters most with dual-mass units.

Conversion kits replacing a dual-mass with a solid flywheel and a sprung-hub disc are cheaper and transmit more vibration - a decision worth making once per platform rather than per vehicle.

Whatever is fitted, flywheel bolts are usually single-use and torque-to-yield.

Yes, and the difference shows in the release bearing, the facing material and the consistency of clamp load rather than in how the parts look.

A cheap release bearing is the commonest reason a budget kit comes back, because it is the item under continuous load whenever the pedal is down.

Facing material determines heat tolerance and judder resistance, and a budget facing fades sooner under repeated slipping.

Consistency of pressure plate clamp load matters on a fleet, where identical vehicles should behave identically.

Against that, the labour cost is the same whichever kit is fitted, which changes the arithmetic decisively in favour of the better part.

For fleets, standardise on one supplier per platform and track how long the kits last - that data settles the question better than any specification sheet.

It is set by duty and driving style rather than distance, and it is one of the clearest driver-behaviour indicators a fleet has.

Wear happens during slip, so the number of pull-aways and gearchanges matters far more than the kilometres.

A laden vehicle slips the clutch harder and longer at every start, so load is the second variable.

Riding the pedal, holding on a gradient with the clutch, and slipping instead of selecting a lower gear will all halve the life.

Two identical vehicles on the same route with different drivers can differ by a factor of two or more, which is worth acting on rather than accepting.

There is no inspection short of removing the gearbox, so tracking replacement intervals by vehicle and driver is the only practical management tool.

Disc orientation and centring, flywheel face condition, spigot bearing, release mechanism free movement, and that nothing is contaminated with oil.

The disc is directional. Most are marked for the gearbox side, and fitting one backwards means the job is done twice - it will not clear the flywheel bolts.

Centring with the alignment tool must be done with the pressure plate bolts torqued evenly and progressively, not one at a time.

The flywheel face should be clean, flat and free of scoring and heat spotting; new friction against a glazed face will judder.

The spigot bearing must be present, correctly seated and free, and it is trivially cheap to renew at this point.

Handle the friction faces with clean hands and degrease the flywheel. A fingerprint's worth of oil is enough to cause judder on take-up.