The GUARDIAN is the strongest optic mounting system on the market. TRU-SEAL(TM) eliminates the need for an added sealing plate. 0-rings on the mounting screws hold the plate watertight to the slide, sealing out moisture, eliminating corrosion in the mounting threads. Radian's STUD-LOK(TM) threaded stud/nut mounting interface is the most secure system on the market. This provides much longer thread engagement, greater hold down power, with increased shear resistance.SIX(TM) BACK-UP SIGHTSSIX(TM) back-up sights (BUS) seamlessly integrate into the Guardian Optic Mounting System providing rapid, reliable, and precise target acquisition in scenarios of red dot optic malfunction. Featuring anti-glare, anti-snag and ultra low co-witness design, SIX(TM) sights lie inconspicuously in wait until you need to deploy them. Like a wingman when things aren't going as planned, SIX(TM) has your six.What's Included:1 - GUARDIAN(TM) Optic Mount and Guard Plate2 - Plate Mounting Screws2 - TRU-SEAL(TM) O-Rings2 - STUD-LOK(TM) Studs2 - STUD-LOK(TM) Self-Locking Sleeve Nuts1 - Back-Up Six Sights