Design - ok, materials - ok, quality control? nope. - Presma AR-15 .223 Barrel Vise Block Rod w/ Torque Block for .750 Barrels

Other reviewers mentioned it. This reaction rod is "clocked" - with the raised "fin" it does not fit into the star chamber. My first thought was that my barrel was clocked, but I've tried it in 4 different uppers, and it's the same everywhere. I got a replacement, and it was identical. Without raising the index fin it "works", but then it has limited use, not what I needed. If you are removing/adding a muzzle device or replacing barrels, you need the "fin" to stabilize, and prevent putting stress on the upper.

Meanwhile I have the 308 version of this, and it fits just fine.