Tapered vs. Gasket Seat

A spark plugs seat creates a seal to the combustion chamber.

There are two seat types available: flat and tapered.

WARNING: Spark plugs with different seat types are NOT interchangeable.

   *Spark plugs with a flat seat must be used in engines designed for a gasket seal. 

   *Spark plugs with a tapered seat must be used in engines designed for a tapered seal.

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Plugs with a flat seat use a crushable gasket to create a seal between the plug and combustion chamber.

All spark plugs with a flat seat should include a gasket on the plug, or in the box. Replacement gaskets can be purchased, and should be replaced every time a plug is re-installed.

As the plug is installed, the gasket starts to meet with the flat face of the cylinder head. Once a plug is hand tightened, torquing (to the proper specifications for your engine) as the final step in the installation process will help ensure the gasket is crushed and has created a tight seal between the plug and combustion chamber.

Plug manufacturers recommend the use of a new gasket any time a plug is re-installed after inspection.

Plugs with a tapered seat use the plugs outer shell to create a seal between the plug and combustion chamber.