We went back and forth with emails, 13 total. I measured everything . That wasn't good enough, so I went to the hardware store and fitted it with a 5/16 - 18 nut and bolt. That wasn't good enough. So they once again pushed the joint tester. Then I finally gave up and ordered it, and suprize it's 5/16 -18. You can't return it , nor will they take the $10 plus shipping $5 off on your purchase. Thru all of this I missed the sale price. It could be a nice shaft, I don't know ! But certainly not a nice experience.