4/15 Tri Rail Barrel Mount for Front Sight Attachment. SKU: MBRTRComplete with 2 Sets of Barrel Adaptors for Standard Barrel, Bull Barrel or Light Weight Barrel* Attaches to Model 4/15 Barrel and Compatible with A2 Front Sight and Bayonet Lug* Made from Aircraft Aluminum with Black Anodizing* Includes Left, Right and Bottom Picatinny Rails, Each with 6 Slots* Easy Installation and Rock Solid Locking* Length 2.6", Width 2", Height 3.3", Weight 3.3oz