This Two-Picatinny-Rails Adapter converts a single Picatinny rail to two side-by-side rails. It can also convert a single Weaver rail to two side-by-side Picatinny rails. It allows you to attach two Picatinny accessories to a single rail. The distance between the two side-by-side rails are 15mm apart. This adapter is designed for airsoft guns, paintball markers, and firearm replicas. You will need a #6-32x1-1/4" screw and a #6-32 nut to fasten this adapter to the gun's Picatinny rail. The screw and nut are not include, but can be easily sourced from your local hardware store (e.g. Home Depot, Lowes, etc.). Airsoft equipment used for illustration of this Two-Picatinny-Rails Adapter are not included. WARNING: Although you can use this mount adapter on your real firearm, we have never tested it with real firearms. We do not know if the firearm recoil will or will not damage this adapter and any accessories attached to it. Use this adapter with real firearms at your own risk.