Magpul Industries Rail Sling Attachment, Quick Detach Sling Mount, Fits Picatinny, Black MAG337-BLK The RSA QD provides a forward attachment point for the Magpul MS4 Sling and other push-button QD slings. Made from corrosion resistant steel" mounts on 1913 Picatinny rail" and places the attachment point at an angle optimized for comfortable two-point sling use while maintaining easy push-button access.