RECESSED

The steel shank is designed to withstand considerable twisting force in proportion to its size, and the tip of the blade is hardened to keep it from wearing. Standard screwdrivers are classified by size, according to the combined length of the shank and blade. The most common sizes range in length from 2 1/2 to 12 inches. There are many screwdrivers smaller and some larger for special purposes. The diameter of the shank, and the width and thickness of the blade are generally proportionate to the length, but again there are special screwdrivers with long thin shanks, short thick shanks, and extra wide or extra narrow blades. When using a screwdriver, you should select the proper size so that the blade fits the screw slot properly. This prevents burring the slot and reduces the force required to hold the driver in the slot. Keep the shank perpendicular to the screw head (fig. 1-48). RECESSED Recessed screws are now available in various shapes. They have a cavity formed in the head and require a specially shaped screwdriver. The clutch tip (fig. 1-47) is one shape, but the more common include the Phillips, Reed and Prince, and newer Torq-Set types (fig. 1-49). The most common type of screw found is the Phillips head. This requires a Phillips-type screwdriver (fig. 1-47). Phillips Screwdriver The head of a Phillips-type screw has a four-way slot into which the screwdriver tits. This prevents the screwdriver from slipping. Three standard-sized Phillips screwdrivers handle a wide range of screw sizes. Their ability to hold helps to prevent damaging the slots or the work surrounding the screw. It is a poor practice to try to use a standard screwdriver on Figure 1-48.-Positioning screwdrivers. Figure 1-49.-Comparison of Phillips, Reed and Prince, and Torq–Set screwheads. a Phillips screw, because both the tool and screw slot will be damaged. Reed and Prince Screwdriver Reed and Prince screwdrivers are not interchangeable with Phillips screwdrivers. Therefore, always use a Reed and Prince screwdriver with Reed and Prince screws, and a Phillips screwdriver with Phillips screws, or a ruined tool or ruined screwhead will result. To distinguish between these similar screwdrivers, refer to figure 1-50. The Phillips screwdriver has about 30-degree flukes and a blunt end, while the Reed and Prince has 45-degree flukes and a sharper, pointed end. The Phillips screw has beveled walls between the slots; the Reed and Prince, straight, pointed walls. In addition, the Phillips screw slot is not as deep as the Reed and Prince slot. Figure 1-50.-Matching cross-slot screws and screwdrivers. 1-29