At least three screw-drivers should be kept, one for large, one for medium, and one for small screws. If its point is wider than the head of the screw, a screwdriver will damage the wood round the head as the screw goes home. On the other hand, trying to force in a large screw with a small screwdriver may break the latter or cut the slot in the screw.

A square-shanked driver to fit a brace is very useful in cases where a number of large screws have to be driven, as a big leverage is obtained. For small screws the Archimedean driver is convenient; and in many cases the ratchet screwdriver makes work easier.

The tip of the screwdriver should have a square, blunt end, thin enough to enter the smallest screw for which it would be used. A point which tapers very quickly towards the end is likely to slip and cut the edges of the slot.

For deep holes a round-shanked driver is needed. A screw-wrench applied to a flat-shanked driver is useful for moving a stubborn screw.

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