Parts of a Distributor – Labeled Diagram with Names

All 15 parts on the diagram

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From the side, taken apart 10

Distributor cap It covers the rotor and the points. Here it is cut through the middle, so you can see the metal inside its towers.
Rotor It sits on top of the shaft. Its metal blade passes close to each outer terminal without touching, and the high voltage jumps the small gap.
Center terminal The coil's high voltage enters the cap here. Its tower is also called the center tower.
Outer terminals There is one for every cylinder. The spark plug wires join them in firing order. This cut shows two of the four.
Carbon button A spring keeps it touching the rotor. The high voltage can then pass from the cap to the turning rotor.
Housing A bowl on a stem, cut through here. The weights and the breaker plate are inside the bowl. Some books call it the distributor body.
Distributor shaft The engine's camshaft turns it through a gear. It turns the cam and the rotor.
Advance weights As the engine speeds up they swing outward against their springs. That makes the spark come earlier. It is called centrifugal, or mechanical, advance.
Vacuum advance A hose brings engine vacuum to it. A diaphragm inside pulls a rod that turns the breaker plate a little, so the spark comes earlier.
Drive gear It meshes with a gear on the engine's camshaft. That is what turns the distributor.

From above, cap and rotor off 5

Breaker points (contact points) They are a switch. Each time they open, the ignition coil makes a high voltage. One contact is fixed and the other is on the end of a moving arm.
Condenser (capacitor) It takes in the surge of current as the points open. That keeps them from arcing. Condenser is the older name. It is a capacitor.
Cam It has one lobe for each cylinder, four here. As it turns, each lobe pushes the points open.
Rubbing block It lifts the arm when a lobe of the cam reaches it. The points then open. It is also called the cam follower.
Breaker plate It can turn back and forth a few degrees. The vacuum advance turns it to change when the points open.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. (1) US Army TM 9-8000, Principles of Automotive Vehicles, 1985, chapter 15, paragraphs 15-3 to 15-7 and figures 15-6, 15-19 and 15-20, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (cap, rotor on top of the cam, center and outer high-tension terminals, distributor shaft driven from a gear on the camshaft, cam lobes, contacts and breaker points, capacitor formerly called a condenser, rubbing block, breaker plate, vacuum advance, a pair of weights for centrifugal advance, distributor housing and body). (2) Florida Automotive Mechanics Curriculum, Engine Tune-Up Service, Unit 4, Secondary Circuit, student guide, Florida State University, 1978, https://archive.org/details/micro_IA41153762_0994 (distributor cap and its towers, center tower, rotor, contact points, condenser, rubbing block, distributor cam, distributor shaft, distributor housing, drive gear, mechanical and vacuum advance mechanisms). (3) Northern New Mexico Community College, Bilingual Skills Training Program, Auto Mechanics, Module 2.0, Ignition System, 1980, https://archive.org/details/micro_IA41153744_0421 (center terminal, outside terminals, carbon button that always touches the rotor, rubbing block, a lobe for every cylinder, contact points, two gears). (4) Wikipedia, Distributor, Contact breaker and Ignition timing, text only (rotor, distributor shaft, cam, contact breaker also called points, carbon button, terminals, hinged weights, vacuum advance, the plate the contact breaker is mounted on, capacitor or condenser). Licence: own work

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

How it works

The parts of a distributor send the ignition coil's high voltage to each spark plug at the right moment. This is an older distributor with breaker points, for a four-cylinder engine.

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From the side

The cap is cut through to show its terminals. High voltage from the coil comes in at the center terminal and passes through the carbon button to the rotor. The turning rotor hands it to each outer terminal in turn. Below, the shaft runs up through the housing from the drive gear. The advance weights and the vacuum advance change when the spark comes.

From above

With the cap and rotor off you look down on the breaker plate. Each lobe of the cam pushes on the rubbing block, and that opens the breaker points. The condenser is wired across the points.

Count the cam's lobes or the cap's outer terminals and you know how many cylinders the engine has.
Later distributors have no points or condenser. A pickup coil and a toothed reluctor do that job.

Questions and answers

What are the parts of a distributor?

A cap with a center terminal and an outer terminal for each cylinder, a rotor, and a housing with a shaft through it. A breaker-point distributor also has a cam, points, a condenser, a breaker plate, advance weights and a vacuum advance.

What does the rotor do in a distributor?

It turns with the shaft and carries the coil's high voltage from the center of the cap to each outer terminal in turn. Its tip passes close to each terminal without touching, and the voltage jumps the gap.

What do the points and condenser do?

The points are a switch that the cam opens and closes. Each time they open, the ignition coil makes a high voltage. The condenser is wired across the points and keeps them from arcing.

Do new cars have a distributor?

Mostly not. Many cars since the early 2000s have a small ignition coil right above each spark plug, so nothing has to hand the spark round.