Outstanding gas block/ flip up front sight. - Yankee Hill Machine Standard Top Mounted Deployable Iron Sight

The YHM-9394 is fantastic. It's well built, easy to mount, and stays in place. When the sight is flipped up there is zero movement or play. It's very sturdy and co-witnessing was easy with my rear back up sights. Another plus is that it clamps so once you have it on there is no need to remove the hider to make adjustments. When folded down, it's completely out of the way allowing for full sight picture through my eotech. Also, it fits perfect for magpul furniture sets. Highly recommend.