Phillips screwdrivers also known as a ˈCross Head Screwdriversˈ because of their shape were invented by Henry F. Phillips in the 1930s for use with his Phillips screws which have a cross shaped recess in their head. Prior to this invention traditional slotted screws and screwdrivers had their limitations. A Phillips head screwdriver has a cross shaped tip with four arms which enable it to engage with the same shaped recess in a Phillips screw. The cross-head design helps to centre the screwdriver in the screw head when pressure is applied and prevents ˈcam-outˈ or slipping. This ˈself-centeringˈ design makes screwdriving easier and more efficient. Phillips screwdrivers are available in different sizes to match the size of the corresponding Phillips screw head they are being used with.