BSPT (British Standard Pipe Taper). Inserted into the end of matching female BSPT threads in pipes and fittings. 1/8"-28x3/4" PIPE PLUGS BSPT SELF COLOUR. 1/4"-19x3/4" PIPE PLUGS BSPT SELF COLOUR. 3/8"-19x3/4" PIPE PLUGS BSPT SELF COLOUR.
eBay