I fitted these recently & had the same pain. I sanded the inside of the end of the tube a bit then inserted the threaded end by hand as best I could. Then I put a sacrificial nut on the end with a stack of washers underneath so I didn?t damage the thread, and used a mallet to drive it in. I?m very certain it won?t come out.
RV-9, Tail Feathers done, Wings almost done.