Tightening spark plugs either too much or too little can damage your engine. Understanding spark plug torque, or tightening specifications, will help you prevent engine leaks and avoid costly mistakes.
Spark plug torque specs depend on the plug's thread size---the diameter of the hole in the engine into which a spark plug screws. Many common plugs have a 14-mm thread, but some engines require other sizes.
Torque specifications vary depending upon the type of material used in the engine, such as cast iron and aluminum. Spark plugs may also come with a gasket, or seal; each type of plug requires different tightening specifications.
Torque is measured in units called foot-lbs. or Newton meters. Each size thread will have a corresponding range of recommended torque. (See the link in the References section for a list of torque specifications for various spark plug types.)
