Ok so turns out its an M8x50/60(ish) bolt. With a blank 'cone' at the end... I think a lot of the bolts on the stilo have this 'locating cone'
I dont know if it is supposed to hold anything inside the box like some sort of cradle or anything. The first maybe 25mm of the hole isnt threaded but after that it is... kind of a weird one.
Anyway, Ive sorted the car it was missing from thanks to a quick trip to the scrappy on my lunch break yesterday just thought I would update you guys on what I found!