The Redding Precision Expanding Die offers the handloader unparalleled control over the I.D. of their case necks (neck tension). Precision Expanding Dies are machined on CNC Lathes and heat-treated to ensure dimensional integrity and durability for a lifetime of use. The unique angled alignment surfaces of the Die Body and Mandrel ensure perfect alignment when assembled and secured with the threaded retention plug and lock ring.Precision Expander Mandrels are machined from high-quality tool steel which is then hardened and precision-ground to their final diameter (size marked on head). They are available in .0005" diameter increments ranging from .0005" thru .0030 below nominal bullet diameter so that neck tension can be fine-tuned to suit the handloader's preference. Precision Mandrels are available separately.