Made of 7075 and hard anodized they are perfectly machined. You will note the unique cross slot channel for the picatinny rail to mate up with. rather than running a single bar through the slot in a picatinny rail this setup places two bars that occupy two slots in the rail. These will NOT move under even the highest recoiling rifles. I would put up against any ring on the market. These are the 4 bolt versions, they also make a 6 bolt version.