Just a little info for any of you planning to install a pyrometer in the tap already in your Jake Brake elbow. Or maybe ya all know it already. The opening is 1/4 NPT so you need a 1/4 to 1/8 NPT bushing if your gauge came 1/8 inch like my Auto Meter did. Was under there pulling the plug when I found the size difference. Called Geno's and they said a bushing was all I needed.