The Denali Slip-On Blackout Covers with their rugged silicone construction, give added protection from rocks and other debris, to your Denali D3 lights, when not in use. Slip them on in places that require aftermarket lighting to be covered on public roads. Once you get to the trails, slip the covers off of your Denali D3 lights and go.The Denali Slip-On Blackout Covers with their rugged silicone construction, give added protection from rocks and other debris, to your Denali D3 lights, when not in use. Slip them on in places that require aftermarket lighting to be covered on public roads. Once you get to the trails, slip the covers off of your Denali D3 lights and go.