(1) The blade of the screwdriver must be ground correctly, and both sides of the blade should be as parallel as possible. If the blade is tapered, the blade easily slides out of the screw slot when turning the screwdriver.
(2) Do not grind the head of the screwdriver too thin or into other shapes than square.
(3) Be very careful when grinding the screwdriver on the grinding wheel, because it will overheat and make the tip of the screwdriver soft. Wear goggles when grinding.