This bolt knob was designed by Area 419 to be the best all around bolt knob for competition and general use. Its main feature is the finger groove which allows you to manipulate the bolt with just your pointer finger without searching for the ideal position each time. Your finger automatically catches in the groove to assure the fastest smoothest bolt manipulation. There are two knurled surfaces located on either side of the groove to give a sure grip. Made in the USA from 6061-T6 aluminum and anodized flat black. Defiance and Remington bolt knobs are threaded 5/16a ^2-24. Remington knobs are 1-5/8a ^2 long to accommodate shorter bolt handles Bergara and CZ 457 bolt knobs are threaded M6x1 and also work on many Accuracy International rifles. Mausingfield bolt knobs are internally threaded 10-32. Will only work on Mausingfield and Nucleus Bolts