Part# KB-NPT-SS-12 ; Stainless Steel 1/2" NPT national pipe taper thread pressure plug. Polished to Kustom Bitz Standard finish that gets right down into the hex socket slot in the pipe plug. These look excellent and will not rust or discolour, the perfect finishing touch for the fussy.

The thread is tappered so as you screw them in it binds against the standard tap thread in the block to form a pressure seal. Usually installed with plumbers thread tape wrapped around the thread of the plug to help it seal.

Make sure you check your sizes required in your engine before you order. They do vary in size.  You may have to retap your block depending on thread type, these are not so easy to source in different thread sizes.