A screwdriver is properly sized when the blade A. fits snugly and completely into the screw’s slot.
When choosing a screwdriver, it is important to choose one that is the correct size for the screw. If the screwdriver is too small, it will not fit into the screw's slot and will not be able to turn the screw. If the screwdriver is too large, it will damage the screw's slot and will not be able to turn the screw properly.
So, one can say that the ideal screwdriver is one that fits snugly and completely into the screw's slot. This will ensure that the screwdriver has the maximum amount of contact with the screw, which will make it easier to turn the screw and will prevent the screw from being damaged.