This is a 1/4" x 28 thread pitch x 1" long alloy screw that has a allen/hex head button top that uses a 5/32" key. This will fit most AR-15 and AR-308 type rifles and pistols.  Included with the screw is 1/4" external tooth lock washer.

The reason for a seemingly long screw is to distribute the stresses from the grip through the steel screw into a long hole in the relatively soft aluminum. Don't use a short screw just because it seems to reach.

We offer both socket cap and button cap style screws.  You can use either and it is a matter of preference.  I prefer the socket cap screws.