Perhaps the most abused of all tools is the screw driver. There are many forms both for bit stock and for hand use. Those for the bit stock, Fig. 193, should be of good quality and well sharpened. In hand screw drivers one may get any style or quality desired. One of the best forms is shown in Fig. 194.

The proper form for the end is a straight even taper from the extreme point to the largest part of the lower end as shown in Fig. 195.

Never stub the end of a large screw driver to make it fit small screws. Nor file a shoulder as shown in Fig. 196. This shoulder not only does it no good but tends to cause the corner of the blade to break more easily than it would if there were no shoulder at this point. A good screw driver properly sharpened, if of the proper size for the screw, will invariably break the head of the screw before being broken. You should have different sizes of screw drivers so that the ends will fit tightly the slots of the screw heads. For elementary work the simple plain tools are the best. The various forms of spiral and ratchet screw drivers are excellent for some purposes, but should not be used until one has become quite familiar with tools in general.

Fig. 193. Bit Brace Screw Driver.

Fin. 194. Hand Screw Driver.

Fig. 195. End of a Properly Sharpened Screw Driver.

Fig. 196. Improperly Sharpened Screw Driver.