4mm shank, about 25mm long with a 3mm allen key for anyone wondering. Also, the cover truly is a pain in the ass to remove. had to loosen up the coolant reservoir, zip tied just about everything out of the way and still took a lot of jimmying. Big issue is the crusty old wiring loom along the right hand side. makes me wonder how easy it will be to pop it back in...with gaskt still in place. Currently contacting people for a new gasket as the half moons were rtv'd and are being very difficult to remove.