2.4.1 Special Screwdrivers Reversible screwdrivers have a different tip at each end of the shank (shaft). The driver handle is removable and fits either end of the shank. The most common reversible screwdriver has a stan- dard (straight-blade) tip at one end and a Phillips tip at the other. Interchangeable bit screwdrivers, Figure 2-22, allow different types and sizes of bits to be mounted to suit the task at hand. Straight-blade, Phillips, Torx®, square socket, and nut-driver tips are available. Some models provide storage in the handle for a number of bits. The screw-holding screwdriver is indispensable for working in close quarters or electrical boxes. Screw-holding drivers are used only to get the screw firmly started. After starting, a conven- tional driver is used for further driving. There are two types of screw-holding screwdrivers: one that holds by means of pressure against the sides of the screw slot and one that has spring-steel fingers to grip the screw head. The relationship of the screwdriver blade and spring-steel fingers is shown in Figure 2-23. Screwdrivers for Torx®, Allen, Pozidriv®, and other special screwhead patterns are available in many sizes and lengths. Figure 2-24 shows these special patterns. receive a drop of oil occasionally. Pliers that are cracked, broken, sprung, or have nicked cutting knives should be discarded and replaced. 2.4 Screwdrivers Screwdrivers are used to drive or withdraw threaded fasteners, such as wood screws, machine screws, and self-tapping screws. Screwdrivers are available in a wide variety of shapes and sizes, Figure 2-20. The right tool is vital for fast and efficient driving and removal of screws. Screwdriver tips are designed to tolerate a limited amount of strain or torque. A screwdriver that is too long, too short, or does not fit the screw properly can waste time and cause damage to the fastener. See Figure 2-21. Goodheart-Willcox Publisher Figure 2-20. Screwdrivers are available in a wide variety of sizes, shank lengths, and tip shapes. State of Ohio Figure 2-21. The tip of the screwdriver must fit the slot properly to avoid damaging the slot or slipping and causing injury. CooperTools Figure 2-22. Reversible and interchangeable bit screw- drivers are versatile, since they allow easy selection of the tip needed for a job. 24 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.