Magpul PTS MBUS Front & Rear Back-Up Sight Set Black Color Polymer *Recommended for airsoft, training, or simulation use only! Front and Rear set made of durable DuPont polymer construction. Spring loaded flip-up design, release lever can be reached on left, right & top position. Suitable for all M4/M16 & AR-Series with standard 20mm RIS/RAS rail. Fully adjustable for windage and elevation.