I tried to edit my post but couldn't. This is to correct my mistake: it's a 6mm screw (coarse thread). Sorry for being most unhelpful in my earlier post. I guess I'm not qualified to use a set of calipers.Yes, I just found mine yesterday and measured it. It's a 4mm fillister head allen screw (SS). Note the length of the threads is only 5mm so Multimike's measurement includes the head.