The ELF SE PRO is identical to the SE Trigger with the addition of a proprietary threaded mounting system. The combination of precision ground threaded bushings, and screws instead of traditional pins provide a rock-solid trigger system. Since their inception, AR platforms have always used pins to mount the trigger and hammer in the lower receiver. Because pins require some play in order to be installed, there is always a little play in the trigger system. This new threaded system adds a level of solid you need to feel to understand the difference. Pull weight is so easy to adjust it can be done in seconds without removing the trigger from your lower receiver. A second-to-none AR Platform drop-in trigger system that is strong and light, made of wire EDM machined, hardened A2 tool steel and lightweight aircraft-grade aluminum. Installation can be done in minutes using the supplied installation screws.