Neck Sizer Dies resize only the neck of case just enough to snugly hold the bullet. This leaves the shoulder and body at their fire-formed dimensions which leads to longer case life and increased accuracy. For use with bolt action rifles only. New brass must be full length sized and fired before it can be neck sized. Set includesa Neck Sizer Die with Expander-Decapping Unit, Expander Die and a Seater Die with Seater Plug. Shellholder sold separately. Notes:Neck Sizer Dies size only the neck of the case ( NOTthe shoulder or body) just enough to snugly hold the bullet for extended case life and accuracy.Expander die expands the case mouth to proper diameter and applies a slight flare (bell) so the bullet can be seated.Seater die applies taper crimp.Lifetime Guarantee from RCBSShellholder not included.