The Aero Precision threaded roll pin is used in multiple applications, including for the bolt catch on their M5 Lower Receivers and for the forward assist on our Upper Receivers. Made from stainless steel, it has a 6-32 thread pitch and is designed to be installed with a 1/16" Hex Key Wrench.Note: This product is already included with their M4E1/M5E1 Enhanced Uppers, M4E1 Threaded Uppers, M5 Upper Receiver and their M5 Lower Receiver. It is not necessary to be purchased separately. This individual product is available for customers who have lost or damaged their existing threaded roll pin.Works With: M4E1 Enhanced Upper Receivers M4E1 Threaded Upper Receivers M5E1 Enhanced Upper Receivers M5E1 Threaded Upper Receivers M5 Lower Receivers DOES NOT work with our M4E1 Lower Receiver DOES NOT work with a standard AR15 Lower Receiver