Poor qualuty - UTG Pro AR15 Carbine Length Drop-in Quad Rail with Extension

The main flaw with this rail is that the top and bottom rail are not designed to be flush together when inatalled. The 4 vertical screws that hold them together, leaves big gaps between the upper and lower rails. They never go together straight. There's always a lopsided mess. The one I used, always had a nosedive in the front. Looking from the side, the right rail was lopsided on a downward angle. You can never level them perfectly. If you try, you'll strip them right out(which I did). Because The rail never goes together straight, the top extended rail never lines up with the upper Receivers rail or the front sight post. You will regret ever buying this rail. The worst rail I ever used.