Expander for copper plumbing

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 c