Brass type core plug for engine. Originally, engines had brass oilway plugs (2K1345) 1/4" hole fitted. These cup type plugs replaced them about 1985. 12.7mm cup type plug about 9.6mm deep. Fits 1/2" hole.

All good engine tuners would remove them for cleaning sludge but these later cup type are much easier to remove and replace. 4 required ON LARGE BORE AND 2 required ON SMALL BORE.