Welcome from South Central Mississippi. Spade bits is what I use, hole saw bits and step bits would work also but to me they would be a slower process. If you are using 1/2" PVC pipe for the arms through bigger PVC I use a 13/16 spade bit for a real tight fit and a 7/8" for a looser fit for 1/2" PVC. It would help if you posted what you are trying to make or how you are trying to make them with the PVC pipe.