Allen Engineering M4 Delta (OPS Green). 5.56mm suppressor based on the modified Ops Inc. 3rd Model, designed to direct-thread onto a 14.5" M4 Carbine using a 3-piece collar (sold separately) that interfaces with the front sight block. Reflex design increases internal volume without adding length. Two-point mounting system reduces flex and offers exceptional return-to-zero. Does NOT include the 3-piece collar. Note: If this product is reflected as in-stock it means it's either physically in-stock or allocated and available (serial number is assigned) at my distributor