Slotted screw drivers are notorious for camming out of the slot (which often destroys the slot and makes driving the screw almost impossible). If you look carefully at most slotted screw drivers, you’ll notice that the tip is beveled - the driving surfaces are not parallel! That slight bevel contributes to cam-out. The driving surfaces on these hollow-ground bits are parallel to improve the fit and reduce cam-out. The Width x Thickness measurements refer to the blade width and thickness - useful when matching the driver and screw since there is so much variation in actual slot dimensions. If in doubt, use the general screw size as a guide.