Here are 10 pieces Holo Krome USA made Stainless socket pressure plugs, 1/8-27 npt, 3/4" taper. Part # 13002. They are app 5/16" long. The socket hex end is 3/16" hex. Stainless is austenitic type. These are new old stock. No vendor packaging or spec sheets. The vendor box in pics is not included.
