Vortex Optics Sport Cantilever 30mm Rings Provides extra rail room for rear Back Up Iron Sights (BUIS) when using the StrikeFire red dot along with the VMX-3T magnifier. The cantilever ring will move the StrikeFire forward about one inch. Use this cantilever mount in conjunction with the Tactical 30mm Ring to mount the Viper XBR crossbow scope. The 1-inch offset of this cantilever mount positions the scope in a forward location, allowing for correct eye relief and head placement. Provides absolute co-witness mounting height of 37 mm. Will work with most 30 mm red dot sights.