RE: ProSpin spinner bolt keeps breaking
PC:
While the Pro-Spin and Spin-Right brand spinners are both good liooking and inexpensive, they are also usually badly out of balance.
Have you checked yours for balance? Might make all the difference in the world.
You could also drill the adapter nut out and retap, replacing the 4 mm screw with a 10-32, or maybe an 8-32 socket headed cap screw.
Bill.