RE: Scale Gee Bee Z question.
Jonas,
The #2 BTN HEAD SCREW refers to the screws that comes with the kit to attach the front part of the legs to the back part. It means #2 Button Head Screw. It has a rounded head 4.8mm in diameter, a thread (#2) of 1.6mm, and a length of 9.6mm (I cut mine down to 6.4mm). I've attached a picture.
Mike