Manufacturer supplied screws that ship with red dot optics aren't always the correct length for a particular firearm. This optic mounting screw kit provides users a variety of Echelon-specific screws to assist in mounting popular red dot optics to the Variable Interface System. This means no messing with cutting down your own screws to the proper length. Blue Loctite is pre-applied for additional strength. CompatibilityScrew Kit 1A: Trijicon RMRScrew Kit 1B: Holosun 507C, 508TScrew Kit 1C: Holsun 509TScrew Kit 2A: Leupold DeltaPoint Pro