If you look around, there are a bunch of 31.8mm bars in the game, especially in this day and age where people are going out in the nature to enjoy a big adventure with wide drop bars.

I have to give my hands up to Nitto for making this gorgeous chromoly 31.8mm stem.

They even have 4 bolts with a bit of an angle (10° to be exact) to get that up right position and for having a horizontal cockpit. They are great for both flat and drop bars. If you like to add an extra drip to your cockpit, the UI-12 stem would be perfect.