Designed to fit G3 and MP5 series rifles (G3SG-1, G3SAS, MP5's, etc...).  This unit has 2 rails (top and side) which allows you to add a scope / red dot, laser and flashlight to your H&K type weapon.  Attaches easily, with allen tool, in minutes - NO modification of your gun is required.  This rail looks great and is the only way to add accessories to some guns.  (Does not work with the PSG-1)