I needed to solder some copper pipe to install water filters. A few of the pieces were small and difficult to hold while cleaning the pipe. So I made this expanding pipe holder for 3/4" pipe. It works great, it turned the most difficult pieces to clean into the easiest. I used a 5/16" bolt because the bolt, washers, and nut, would all fit inside the pipe. The flexible parts expand slightly to grip the pipe as you tighten the nut. Then you put the end of the bolt in a drill and use sandpaper to clean the pipe as it spins.

The inner pieces are generic flexible TPU filament, at first I tried to print the flexible piece as one piece, it didn't adhere to the bed, so I made it a two piece unit and it prints easily. The two outside cones are PLA. All parts are printed slow with 100% infill. You need to print two flexible TPU parts and two PLA parts.