Spark plug torque is the recommended amount of force to use when installing spark plugs so that they are not loose or overly tight, either of which prevents them from functioning properly. Torque is measured by a torque wrench, a special tool that expresses force in units of foot-pounds.
The recommended torque settings for spark plugs differ depending on the style of spark plug, the thread diameter, and the material of the engine block. Most spark plug manufacturers provide a chart indicating the proper torque settings for different situations. Improperly tightening a spark plug affects its ability to remove heat from the combustion chamber, which can lead overheating and permanent engine damage.