3/8″, sharkbite push to connect endstop plug, easy way to cap copper, cpvc or pex pipe in any combination with no soldering, clamps, unions or glue, perfect solution for pressure testing a home, reusable, just insert the pipe & the stainless steel teeth bite down & grip tight, while a specially formulated o-ring compresses to create a perfect seal, disassembly is just as fast using the simple disconnect tool, can be rotated after assembly for easier installation in tight spaces, certified for potable water supply & hydronic heating applications, use to conform to california ab1953 low lead & vermont s152 low lead laws.