Trijicon ACOG Thumb Screw. This part of Trijicon is a direct replacement for the thumbscrew included with the ACOG. With this part of Trijicon you no longer have to worry about losing or breaking your lens because of the recoil. The Trijicon ACOG Thumbscrew is here to stay because when you're using your ACOG and something goes awry with it you can easily tighten it back in place. So when you need to replace your Trijicon Thumbscrew look no further than the Trijicon ACOG Thumbscrew. This part of Trijicon comes with a replacement ground glass so that you can get your Trijicon ACOG Thumbscrew back in shape. TA53: Trijicon TA53 ACOG Thumb Screw