I am pretty sure you refer to the little thing next to the center vent that looks like it slides up or down, but is actually the edge of a rotary knob.
I was thinking more of that lump of wood we’ve all got in our shops. None of the surfaces are flat, or parallel, and it’s too oil soaked to burn in the fireplace, but somehow… it comes in handy every now and then.
Gary has been likened to many things over the years, but never until now as a very large square “plank”!
In fact many punters speak highly of him in the Smoke.