The JP Speed Hammer is not compatible with standard AR-15 trigger parts. The new design in made from laser cut cryogenically treated A2 tool steel, hardened to 58 Rockwell all the way through, not just on the surface like conventional hammers. It also features a precision pressed in stainless pin boss for accurate alignment. Improved metallurgy, precision geometry and notch preparation result in a durable high performance part. Now supplied with a "D" spring to retain standard grooved trigger pins.