Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2471085.

This is a P Clip for 20mm Conduit. It's designed to suit corrugated 20mm conduit (which actually seems to be about 21mm outside diameter), but should be suitable for rigid PVC tubing also. The internal diameter when printed is 22mm, which clamps down to 21mm when the screw is tightened.

It needs one countersunk screw for mounting (it would suit a 6g x 5/8" wood screw for example).

I printed this in PLA, and found it was flexible enough to push onto the conduit.