www.phcppros.com/articles/6013-john-guest-usa-prolock-end-caps

John Guest USA ProLock End Caps
September 14, 2017
Designed for use in the plumbing market, the new ProLock End Caps are available in 3/8- to 1-inch CTS sizes.
The end caps can act as emergency water stoppers and are used for pressure testing rough-ins and temporarily capping off installations. Its body is manufactured from high quality engineered plastic allowing the black caps to be UV resistant outdoors as well. Suitable for use with copper, PEX or CPVC pipe, these products require no tools to make secure, leak-proof connections.
The product is lead-free, and has a 25-year warranty.
John Guest USA.