SCREWDRIVERS

which slips over the die block and has a compressor screw and a cone that forms a 45-degree flare or a bell shape on the end of the tube. The screw has a T-handle. A double flaring tool has the additional feature of adapters, which turn in the edge of the tube before a regular 45-degree double flare is made. It consists of a die block with holes for 3/16-, 1/4-, 5/16-, 3/8-, and 1/2-inch tubing; a yoke with a screw and a flaring cone; plus five adapters for different size tubing, all carried in a metal case. REVIEW QUESTIONS Q37. What are pipe cutters used for? Q38. What are tube cutters used for? Q39. What are flaring tools used for? SCREWDRIVERS LEARNING OBJECTIVES: Identify the different types of screwdrivers. List the safety precautions that apply to screwdrivers. A screwdriver is one of the most basic of handtools. It is also the most frequently abused of all hand tools. It is designed for one function only—to drive and to remove screws. A screwdriver should not be used as a pry bar, a scraper, a chisel, or a punch. STANDARD There are three main parts to a standard screw- driver. The portion you grip is called the handle, the steel portion extending from the handle is the shank, and the end that fits into the screw is called the blade (fig. 1-71). The steel shank is designed to withstand con- siderable 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. 1-72). 1-44 Figure 1-70.—Flaring tools.