I am a surveyor by profession, and have made a few out of broken carbon fiber prism and GPS rover poles. The top sections are around 3/4" tube. I found some bushings that were the correct OD fie the tubes and had a 5/16 female thread. I epoxies them into the tube and then use a 5/16 stud to go to the bow. The other end is already threaded with 5/8 to go to surveying implements. I bought a knurled brass nut for on the ends. I'll take a picture of one if I remember.