The RCBS 19108 refers to a 3-Die Roll Crimp Set, specifically designed for loading straight-wall cartridges. This complete set is comprised of a steel Sizer Die, an Expander Die, and a Seater Die.The steel Sizer Die has a dual function, which encompasses case sizing and de-priming. Its primary role is to restore the case to the desired dimensions and simultaneously remove the spent primer.Next in the set is the Expander Die. Its main purpose is to widen the case to the required diameter so it can comfortably accommodate the bullet. Additionally, it lavishes the case mouth with a slight flare or bell to facilitate bullet feeding.The final element is the Seater Die. This tool securely seats the bullet into the case and imparts a roll crimp to ensure the bullet stays intact. Important to note is that for effective functioning, the cases need to undergo lubrication prior to use.