I have made many types of shell case neck forming dies over the years. If they are round, then the question is always how to hold them properly on a shop/arbor press. I have had this design in the back of my mind for many years. It is a large set of plates that have an eight inch hole in the middle. I can now use 8 or 6 or 4.5 inch adapters to get the exact hole sizes I want. Each die I crate now will now conform to this set of plates and adapters to hold it. Fortunately for me, I have the material, engineering skills, CNC Mill and time that have allowed this vision to emerge. This example has a 3 inch hole die in place. I also happen to do much work pressing bearings into and out of housings - in addition to reforming shell cases back to original specifications. I will add many more custom hole sizes over time. I can make more of these if anyone else desires the finest tools available for their work. A warning though, this kind of tooling is not inexpensive.