This Spigot Mount is designed to be used with the MPA BA Lite Chassis, Hybrid Chassis, ESR and our newer BA Chassis and Comp Chassis. The design includes a picatinny rail on one side and a RAT adapter plate on the other. This can be retrofitted to any MPA chassis with the oval spigot mount cut on the front of the chassis. Masterpiece Arms Spigot Mount SPIGOTMT-V4