The Handyman's Pocket Book: Screws (Metal) and Nuts.

These are used chiefly for joining metal together, though they have a fairly wide use in woodwork also.  In metal work the metal can be tapped to hold the thread of the screw, in which case the hole in the metal beneath the head is of clearance size as shown in Fig. 1, A.  Alternatively both holes can be of clearance size as at B, Fig. 1, in which case it is necessary to fit a nut over the screw.  A washer is generally used under the nut, and sometimes beneath the screw head as well.  In most cases the simple ring, Type C, Fig. 1, is satisfactory, but the spring form, D is useful in that it helps by friction to prevent any tendency for the nut to loosen.

SIZES.  Although there are several kinds of threads for screws, the chief kinds are the Whitworth and the B.A., the latter being the fine thread of the two.  Whitworth screws are known in fractional sizes of an inch, and the usual sizes are: 1/8, 5/32, 3/16, 7/32, 1/4, 9/32, 5/16, 3/8, 7/16, 1/2 in.  Many ironmongers do not stock the thirty-second sizes.  Lengths vary from 3/8 in. up to 3 in.  B.A. screws are known by numbers, 0-10.  As a rough guide they may be compared with fractional inch sizes from 1/4 in. to 1/16 in.  The two are not interchangeable as the pitch of the thread is different.  Lengths are generally reckoned in inches - 1/4 in. to 1 1/2 in.

VARIETIES.  Apart from the thread, screws are made in various metals, the chief (for general use as distinct from engineering) being mild steel and brass.  There are also many kinds of heads, the chief being shown in Fig. 2.  Sizes are known by the over-all diameter of the thread, and the length.  The dotted lines show where the length is reckoned from.  Thus when ordering screws ask for "one dozen 3/16 in. countersunk iron, 1 1/2 in. metal screws, Whitworth."

In addition to the above metal screws are carriage bolts used mostly for joining wood parts together or metal to wood (see Fig. 3).  There is a square shank beneath the head which prevents it from turning round when the nut is tightened.  When this fits in metal a square clearance hole is needed; in wood the hole is generally bored a clearance fit for the round part of the shank.  A blow from the hammer then makes it bite its way into the wood - at any rate in softwoods.  In hardwoods it may be necessary to ease the holes with a chisel.  Heads are generally of the mushroom type (A), countersunk (B), cheese (C), and cone (D).  When used for wood a washer should always be placed beneath the nut as otherwise it will bite into the wood.

Handrail bolts (Fig. 4) are used for joining a handrail to a newel post.  They are also useful for a large mitre such as in a wood curb.  Recesses are chopped down from the surface to receive the bolts and clearance holes bored in at right angles in the mitre.  These holes must run beyond the nut holes.  The square nut is dropped into its recess and the bolt screwed into it.  The round nut is passed into it recess and the bolt entered into its hole.  The round nut is turned by pressing a screwdriver into the recesses around its edge.  There should be a washer between it and the wood.  Final tightening is by means of a special punch (D) which is rather like a bent screwdriver.  This is placed in the slots on the nut and tapped with the hammer.  As a rule a couple of dowels are also bored into the mitre to prevent the joint from twisting.

NUTS.  The kinds in general use are: hexagon (A), square (B), wing (C), and dome (D) (see Fig. 5).  The last should always have a comfortable clearance between the end of the screw and the bottom of the hole in the nut.

When bolts are used for joining wood together the holes should always be of clearance size so that the bolts can be passed straight in without turning.  A washer is used between the nut and the wood.

STUDDING.  Sometimes it is necessary to join heavy timbers with long bolts, and it may not be possible to obtain the last named as a standard fitting.  The best plan is to use what is known as studding which is simply a rod of metal threaded for the whole of its length.  The usual standard sizes are available - 1/4 in., 3/16 in., 3/8 in., 1/2 in., and the length is generally 12 in.  It is necessary to use a nut at each end, and washers are required.  Make sure that the nuts have the same thread as the studding.