While all our other BBQs have teltrus installed, the 22.5” WSM didn’t because the provided thermometer in the lid seemed to work fine. However, recently its been showing 150F when its cold and ended up about 30 degrees out most of the time so it was time to swap it out.
The teltru requires a 22mm hole to be drilled in the BBQ. I use a stepped HSS drill bit to gradually work up to it from the 6mm hold that’s in the lid for the factory thermometer. A constant stream of WD40 onto the drill as its working ensures a neat hole and doesn’t chip the enamel too much.
Above the hole you can see the guide hole for the mount for the thermometer. On the small WSM this is close enough to the main hole that you can combine them into a single 22mm hole. On the big one this is a problem, which I solved by drilling out and fitting a single 6mm stainless steel bolt. I also paint round any cuts with high temperature black paint to protect against any rust.
This fits behind the teltru easily and looks pretty cool.
This shot shows the inside of the lid with the bolt and thermometer stalk poking through.