I'm tinkering around with a little project that will have 2  cables 
(like microphone cable size) entering a metal box.    I can use rubber 
grommets to protect the cables, but  they could accidentally pull 
through the grommet.

I could use zip ties, or hot glue, or knot the cable inside the box to 
prevent a pull through, but that's kind of rinkey dink.

I've seen hard plastic things that fit the chassis hole and when the 
cable is passed through, a little thing on the inside clamps down to 
lock the cable.   Anybody know what these things are called?   I'd like 
to look on ebay, but have no idea what item to search for.

Tnx, Steve KW3A