What is a spark plug thread size?

The thread size of a spark plug typically varies depending on the engine it is designed for, but common sizes include 14mm, 18mm, and 10mm. Most automotive spark plugs feature a 14mm diameter with a 1.25mm or 1.5mm thread pitch. It's essential to match the thread size and pitch to the specifications of the engine to ensure proper fit and function. Always consult the vehicle's manual or manufacturer specifications for the correct spark plug thread size.