Dillon Precision trim dies are used just like a standard size die. The big difference is that while you are pushing the case into the die to size it, a 1/4 horsepower electric motor driving a carbide cutter is trimming the case to length. Trim dies, in all calibers, are compatible with both the older RT1200 Trimmer as well as the current RT1500 Trimmer.NOTES: The following trim dies MUST be used with a short trim die toolhead: 300 Blackout, 6.8 SPC and 7.62 x 39mm.Trim dies include the lower die lock ring. Upper die lock rings are not included with the trim die, but are available separately.