There are four types:

1. M10 × 1 - for motorcycles, chainsaws, lawn mowers.
2. M12 × 1,25 - for motorcycles.
3. M14 × 1,25 - for most modern cars.
4. M18 × 1,5 – for cars of early manufacture years, cars with gas fueled reciprocating engines.

As a rule, there are three groups of spark plugs based on the thread length:

1. Short thread - 12 mm.
2. Medium thread - 19-20 mm.
3. Long thread - 25 mm.

The more powerful the engine, the longer must be the thread of the spark plug. A long thread creates a large contact area of the spark plug with the engine cylinder head, and therefore a large heat exchange coefficient.