A core part of the ZERO Sizing Die design is a precision ground, full-length mandrel. Designed to provide the greatest consistency in neck tension, these were also meant to be interchangeable, allowing the reloader to select the amount of neck tension that works best for them. Our mandrels are ground 17-4PH Stainless Steel, and black nitrided for smooth and long-lasting operation. These kits include FOUR mandrels, so when combined with the mandrel that came with your ZERO M-Series or S-Series sizing die, give you .0005 neck-tension increments from .0005 to .0025.