These are for connecting a branch to an existing run of pipe. You'd clamp one to a pipe with the gasket carefully positioned, then drill through the wall of the pipe with a 1/4" drill. (Needless to say, it's wise to shut off the water supply first.)
All the plumbing in my house is copper, so I really have no use for these. Anyway, they can go in the drawer where I keep some pipe fittings. Perhaps I'll find a strictly mechanical use for them some day.
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