Primary Arms SLx MD-21, Microdot, 21MM Objective, Red ACSS CQB Reticle, Fits Aimpoint Micro Footprint, Anodized Finish, Black PA-SLX-MD-21-ACSS The SLx MD-21 is an advanced micro dot sight that incorporates the latest technologies and materials to deliver exceptional CQB performance. Weighing only 5 ounces, the SLx MD-21 is both lightweight and rugged, featuring upgraded mounting hardware for guaranteed rigidity and precision when you need it most.