NPT Explained

National Pipe Thread (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings.  The taper on NPT threads allows them to form a seal when torqued.

To determine the NPT size for an engine anode’s brass plug, measure the outside diameter (OD) of the threaded section of the plug then select the corresponding NPT size from the table below.

For example, if a plug’s thread OD measures approximately 3/4", the corresponding NPT size is 1/2.