The steel .38 set is missing the expanding die which also did the decaping. The nut and pin you have in the box mounted to the nose of the expander. I have a set just like that. RCBS no longer supports that style expander, but they will send you a "kit" that will convert the sizing die to hold a modern decaping rod, and any standard modern expander will fit the expanding die. I elected to get a cowboy set expander for use with lead bullets.