Brilliant. I (honestly) had no clue. You're still welcome to make fun of me if you want.
That even looks similar to the tool being used in the workshop manual.
If I can account for the distance between the top of the stud and the housing (because the base of that gauge isn't going to fit through the hole) then that will totally work.
Good grief, thank you - I really did just slap myself in the forehead.
