Designed to fit G3 and MP5 series rifles (G3SG-1, G3SAS, MP5's, etc...).  There mounts allow you to much needed accessories such as a scope / red dot, laser and flashlight to your H&K type weapon.  Attaches easily - NO modification of your airsoft gun is required.  These rails look great and are the only way to add accessories to some guns.  (Does not work with the PSG-1)