Parts of a Strut Assembly – Labeled MacPherson Strut

All 12 parts on the diagram

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The whole strut 4

Coil spring It carries that corner of the car. It sits squeezed between the upper and lower spring seats.
Strut body The shock absorber is inside it. The piston rod slides in and out of its top. Also called the strut housing.
Lower spring seat The bottom of the spring rests in it. It is welded to the strut body.
Lower mount Bolts to the steering knuckle. That sends the wheel's up-and-down movement into the strut.

The top end, pulled apart 8

Strut mount (upper mount) Fixes the top of the strut to the body. It carries that corner's load. Service books also call it an insulator.
Piston rod nut Holds the strut mount and the spring's upper seat. They sit on the end of the piston rod.
Bearing Lets a front strut and its spring turn with the wheel. It does so when the car is steered.
Upper spring seat The top of the spring fits into it. Unlike the lower seat it is a separate piece, held in place by the strut mount.
Spring insulator A ring of rubber that the spring's end coil presses against.
Jounce bumper (bump stop) The strut meets this rubber, not metal. That is when the wheel comes up as far as it can go.
Dust boot (dust shield) Keeps dirt and stones off the piston rod and the seal. The seal is at the top of the strut body.
Piston rod Moves in and out of the strut body. That happens as the wheel rises and falls. Everything above is stacked on it.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. The three books were read as the passages a full-text search returns. (1) Birch, Automotive Suspension and Steering Systems, https://archive.org/details/automotivesuspen0000birc (upper mount or upper strut mount, upper and lower spring seat, spring insulator, coil spring, jounce bumper, dust shield, piston rod, strut body or housing, lower strut mount to the steering knuckle, bearing). (2) Motor Domestic Front End and Brake Service, 1987-91, https://archive.org/details/motordomesticfro0000unse (strut mount, upper mount, upper and lower spring seat, spring insulator, jounce bumper, dust boot and dust shield, thrust bearing, strut body, strut shaft nut and piston rod attaching nut). (3) Chilton repair manual, Honda Accord and Prelude 1984-91, https://archive.org/details/chiltonbookcompa0000unse_l8b9 (upper spring seat, coil spring, dust cover, rubber bump stop, lower strut mount). (4) US Army TM 9-8000, Principles of Automotive Vehicles, paragraph 30-8, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (the strut houses the shock absorber and links the wheel and the body; coil spring between upper and lower flanges). (5) Wikipedia, MacPherson strut and Strut, text only (top mount to the body; the bearing where the strut is a steering pivot). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's strut, nothing traced. Licence: own work

How it works

A strut assembly is a shock absorber and a coil spring built into one unit that links the wheel to the car's body. The second view pulls its top end apart.

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Big parts first, then the stack on top

The whole strut shows the four parts you can see on the car: the coil spring, the strut body, the lower spring seat and the lower mount. The second view takes the top end apart along the piston rod. From the top: the nut, the strut mount, the bearing, the upper spring seat, the insulator, then the jounce bumper and dust boot over the rod.

The spring is held squeezed between its two seats. A strut is taken apart only with a spring compressor.
Bump stop and jounce bumper are two names for one part; so are dust boot and dust shield.

Questions and answers

What are the parts of a strut assembly?

From the top: the piston rod nut, strut mount, bearing, upper spring seat and spring insulator; then the coil spring with the jounce bumper and dust boot inside it; then the piston rod, the strut body with its lower spring seat, and the lower mount.

What is the top of a strut called?

The strut mount, or upper mount. Its studs bolt up into the car's body. On a front strut a bearing under it lets the strut turn when the wheels are steered.

What is the difference between a strut and a shock absorber?

A shock absorber only damps the spring's bouncing. A strut has the shock absorber inside its body and also carries the spring and links the wheel to the body, so it is part of the car's structure.

What does the bump stop on a strut do?

It is a rubber cushion on the piston rod. When the wheel travels up as far as it can, the strut meets the rubber and not bare metal. Service manuals call it the jounce bumper.