The EMR-H features a slightly curved button or dimpled surface to fit the natural curvature of your finger. The form fitting curve, along with horizontal serrations, create a self-centering surface that inhibits the finger's vertical movements. The EMR-H has a mil-spec through hole for the magazine catch's shaft and is only 0.02" taller than the factory magazine release button. When installed, the EMR-H has minimal protrusion above the mag release button fence on most forged receivers. Machined from 4140 bar stock, it is QPQ coated Proudly made in the USA. AR-15/M16 Through hole magazine release button Curved and serrated surface 4140 ste Mfg: Forward Controls Design