
I’m after fitting a t-handle to the top of a hollow metal tube. The t-handle has a has a thread hole in it, 3/8” - 16 thread. I am trying to find a fitting that will slot into the tube and expand to hold it secure, that I can then thread the correct size bar into it to screw the t handle onto. (Hope that makes sense…

I’ve been searching for all sorts of expanding / expansion fittings and can’t find anything suitable. Any ideas if this exists and what the correct terminology would be to search for?
Dodgy diagram to try and show what I’m trying to do!

TIA