Four different Versions that go on your Alpha Trooper (ALL VERSIONS) Rail and add a Diopter sight similar to that of a SIG 552. All versions fit on the rail (sanding of the print may be required) and are locked in place by an m3 screw. additional just for optics an M4 screw and an M3 screw can be added.
Version 1: Just the Diopter.
Version 2: Diopter plus 75mm Picatinny Rail
Version 3: Diopter plus 95mm Picatinny Rail
Version 4: Diopter plus flatbed with holes for 10cm Worker picatinny rail.
Works great with my SIG 552 Front!