This item is pounded into wood where it is flush with the surface.
It is also threaded to receive a male screw. But what do you call
It? See attachment

We call them mollies, but I'm sure one of the actual expert in this area will be able to give you the name.

pastor1189, please tell us how and where and for what plumbing item this fitting was used.

These are used in wood.

I found it it is called a T nut. Thanks gang