FAB Defense FRBS Offset Black Folding Backup Sights Kit. Product Advantages: Designed as a back-up sighting solution for use in conjunction with magnification lenses during CQB scenarios Sleek design with minimal protruding parts No tools needed for a quick and easy elevation and wind adjustment RBS - Rear Back-up sight can be manually adjusted for windage FBS - Front Back-up sight can be manually adjusted for elevation Available in both right and left side variations Durable fiberglass reinforced polymer and metal construction Compatibility: 1913 MIL-STD Picatinny rail. Specifications: Length: 52 mm Width: 32 mm Height: 14 mm Length deployed: 30 mm Height deployed: 42 mm Weight: 30 gr