I made these. I really like having the weight of these inside the socket. they dont' flex at all obviously and I can use them as anvils to then close up the sockets to fit the tubes tightly. As the end relief suggests, these interlock within the shell. The relief is cut with a hole saw on the mill. The other ends of these bars will be turned to the other sizes as needed. The middle bar is for 22mm chainstay sockets.
Please excuse the dimpler testing left overs in the background!
Blacksmithing by
Duane Draper, on Flickr