It's a screw driver to hold Hexagonal screwdriver head.It's a screw driver to mount Hexagonal screwdriver head. There is a space in the interior for storing the screw head, the long and short. I suggest to not mount and dismount heads too often, it's only plastic :), it's better to mount a adaptator head. I have made it in ABS.Hexagone size is 7mm inside.there is 2 version the smaller is 20mm large and the larger is 25mm large (XL parts), depend of your hands.Print 1 of each or the plate then use 3x M3 20 or 25mm long + nuts the cover is just held by the 2 sides.