Autolite - Crush Gaskets

There are two styles of spark plug. A "tapered seat" spark plug has an angled shoulder that makes contact with the head, and seals the plug using the tension on the threads of the spark plug’s shell. The other style of plug uses a "crush gasket" that looks like a washer. This gasket seals the flat part of the plug's shoulders, to the flat part around the spark plug hole.