Mine are regular clamps from diywake.com that we welded aluminum tubing too a mount for the poles to go down in, the pole holder bolts to the clamp and acts as a set screw so nothing can rotate orn move at all. Drilled and tapped thru just so we could snug the pole up and not have any rattle. My poles are just regular electrical conduit.

Prior to this I used metal hose clamps. Those also worked pretty good.