These M3 screws are used for mounting the Scorpion HK-22mm, HK-30mm, 22mm, 30mm, and 40mm series motors. Included in this kit are two 3x0.5x8mm socket head screws and two matching flat washers. The flat washers have an outside diameter of 6.75mm and are 0.65mm thick. The backplate of the HK-22mm and HK-30mm 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 backplate and the washer.