It is used to install or remove spark plugs from internal combustion engines, specifically plugs that require a key of this size. And
The 21mm spark plug wrench is a tool specifically designed for installing and removing spark plugs in internal combustion engines. It is characterized by the size of the head hole that matches the size of the spark plugs used in the engine. This wrench usually comes with a handle that makes it easy to control and direct force to install or remove the spark plugs easily. This wrench is an important part of an automotive and mechanic's toolkit, used for routine vehicle maintenance and engine repairs.