See-through design allows for use of the original iron sights * Top/Bottom 2-piece Innovative Design with Lower/Upper Pieces Mating/Locking Feature * Includes 20 left/right/bottom slots and 31 or 20 top slots * Great zero-retention capability for all accessories installed on the rails * Easy installation with no modification to the barrel involved; measures 15 inch 15 by 2.3 by 3.2 inches (L x W x H)