These screws are used for mounting the Scorpion HK-22mm and 30mm series helicopter motors. Included in this kit are two 3x0.5x6mm socket head screws and two matching flat washers. The flat washers have an outside diameter of 6.75mm and are 0.65mm thick.
The back-plate of the Scorpion motors are 3mm thick, so to get the right size screw, add 4mm to the thickness of your motor mount plate to get the proper length screw. This will allow for the thickness of the motor back-plate and the washer.