Case forming dies are designed to reduce the case by steps to eliminate case stress or collapse and to prolong case life. There will be one or more form dies for each caliber. After forming and trimming, cases must then be full length sized, using the full length sizer in the reloading die set for the finished caliber. RCBS does not recommend using full length sizer dies for the actual case forming process. Case forming dies (threaded standard 7/8 x 14 unless otherwise noted) will withstand the normal case forming pressures encountered but are not intended to swage the base of the case. When that is required, a special Base Form die is needed. Base Form dies are unthreaded and require the use of a 3-ton arbor press.