OK, Bryan.
The keeper thread in the end of the rod is an M6 coarse thread
. I just tried some different screws I had in the shed.
BTW a 1/4" camera mount thread is the same as 1/4" UNC which is the same as 1/4" W.
If ever there was evidence that is was an american design made in asia it's the mixing of units and thread systems!
Al.