CHAPTER V.--FASTENING DEVICES.

Bolts are usually designated for size by their diameters measured at the cylindrical stem or body, and by their lengths measured from the inner side of the head to the end of the thread, so that if a nut be used, the length of the bolt, less the thickness of the nut and washer (if the latter be used), is the thickness of work the bolt will hold. If the work is tapped, and no nut is used, the full length of the bolt stem is taken as the length of the bolt.

A _black_ bolt is one left as forged. A finished bolt has its body, and usually its head also, machine finished, but a finished bolt sometimes has a black head, the body only being turned.

A square-headed bolt usually has a square nut, but if the nut is in a situation difficult of access for the wrench, or where the head of the bolt is entirely out of sight (as secluded beneath a flange) the nut is often made hexagon. A machine-finished bolt usually has a machine-finished and hexagon nut. Square nuts are usually left black.

The heads of bolts are designated by their shapes, irrespective of whether they are left black or finished. Fig. 370 represents the various forms: _a_, square head; _b_, hexagon head; _c_, capstan head; _d_, cheese head; _e_, snap head; _f_, oval head, or button head; _g_, conical head; _h_, pan head; _i_, countersink head.

The square heads _a_ are usually left black, though in exceptional cases they are finished. Hexagon heads are left black or finished as circumstances may require; when a bolt head is to receive a wrench and is to be finished, it is usually made hexagon. Heads _c_ and _d_ are almost invariably finished when used on operative parts of machines, as are also _e_ and F. Heads _g_ are usually left black, while _h_ and _i_ are finished if used on machine work, and left black when used as rivets or on rough unfinished work.

The heads from _e_ to _i_ assume various degrees of curve or angle to suit the requirements, but when the other end of the bolt is threaded to receive a nut, some means is necessary to prevent them from rotating in their holes when the nut is screwed up, thus preventing the nut from screwing up sufficiently tight. This is accomplished in woodwork by forging either a square under the head, as in Fig. 371, or by forging under the head a tit or stop, such as shown in Figs. 372 and 373 at P. Since, however, forging such stops on the bolt would prevent the heads from being turned up in the lathe, they are for lathe-turned bolts put in after the bolts have been finished in the lathe, a hole being subsequently drilled beneath the head to receive the pin or stop, P, Fig. 372, which may be tightly driven in. A small slot is cut in the edge of the hole to receive the stop.

Bolts are designated for kinds, as in Fig. 374, in which _k_ is a machine bolt; _l_ a collar bolt, from having a collar on it; _m_ a cotter bolt, from having a cotter or key passing through it to serve in place of a nut; _n_ a carriage bolt, from having a square part under the head to sink in the wood and prevent the bolt from turning with the nut; and _o_ a countersink bolt for cases where the head of the bolt comes flush.

The simple designation "machine bolt" is understood to mean a black or unfinished bolt having a square head and nut, and threaded, when the length of the bolt will admit it, and still leave an unthreaded part under the bolt head, for a length equal to about four times the diameter of the bolt head. If the bolt is to have other than a square head it is still called a machine bolt, but the shape of the head or nut is specially designated as "hexagon head machine bolt," this naturally implying that a hexagon nut also is required.

In addition to these general names for bolts, there are others applied to special cases. Thus Fig. 375 represents a patch bolt or a bolt for fastening patches (as plate C to plate D), its peculiarity being that it has a square stem A for the wrench to screw it in by. When the piece the patch bolt screws into is thin, as in the case of patches on steam boilers, the pitch of the thread may, to avoid leakage, be finer than the usual standard.

In countersink head bolts, such as the patch bolt in Fig. 375, the head is very liable to come off unless the countersink in the work (as in C) is quite fair with the tapped hole (as in D) because the thread of the bolt is made a tight fit to the hole, and all the bending that may take place is in the neck beneath the head, where fracture usually occurs. These bolts are provided with a square head A to screw them in by, and are turned in as at B to a diameter less than that at the bottom of the thread, so that if screwed up until they twist off, they will break in the neck at B.

Instead of the hole being countersunk, however, it may be cupped or counterbored, as in Fig. 376, in which the names of the various forms of the enlargement of holes are given. The difference between a faced and a counterbored hole is that in a counterbored hole the head or collar of the pin passes within the counterbore, the use of the counterbore being in this case to cause the pin to stand firmly and straight. The difference between a dished and a cupped is merely that cupped is deeper than dished, and that between grooved and recessed is that a recess is a wide groove.

Eye bolts are those having an eye in place of a head, as in Fig. 377, being secured by a pin passing through the eye, or by a second bolt, as in the figure. When the bolt requires to pivot, that part that is within the eye may be made of larger diameter than the thread, so as to form a shoulder against which the bolt may be screwed firmly home to secure it without gripping the eye bolt.

Fig. 378 represents a foundation bolt for holding frames to the stone block of a foundation. The bolt head is coned and jagged with chisel cuts. It is let into a conical hole (widest at the bottom) in the stone block, and melted lead is poured around it to fill the hole and secure the bolt head.

Another method of securing a foundation bolt head within a stone block is shown in Fig. 379; a similar coned hole is cut in the block, and besides the bolt head B a block W is inserted, the faces of the block and bolt being taper to fit to a taper key K, so that driving K locks both the bolt and the block in the stone. When the bolt can pass entirely through the foundation (as when the latter is brickwork) it is formed as in Fig. 380, in which B is a bolt threaded to receive a nut at the top. At the bottom it has a keyway for a key K, which abuts against the plate P. To prevent the key from slackening and coming out, it has a recess as shown in the figure at the sectional view of the bolt on the right of the illustration, the recess fitting down into the end of the keyway as shown.

Another method is to give the bolt head the form at B in Fig. 381, and to cast a plate with a rectangular slot through, and with two lugs A C. The plate is bricked in and a hole large enough to pass the bolt head through is left in the brickwork. The bolt head is passed down through the brickwork in the position shown at the top, and when it has passed through the slot in the plate it is given a quarter turn, and then occupies the position shown in the lower view, the lugs A C preventing it from turning when the nut is screwed home. The objection to this is that the hole through the brickwork must be large enough to admit the bolt head. Obviously the bolt may have a solid square head, and a square shoulder fitting into a square hole in the plate, the whole being bricked in.

Figs. 382 and 383 represent two forms of hook bolt for use in cases where it is not desired to have bolt holes through both pieces of the work. In Fig. 382 the head projects under the work and for some distance beneath and beyond the washer, as is denoted by the dotted line, hence it would suspend piece A from B or piece B from A. But in Fig. 383 the nut pressure is not beneath the part where the hook D grips the work, hence the nut would exert a pressure to pull piece B in the direction of the arrow; hence if B were a fixed piece the bolt would suspend A from it, but it could not suspend B from A.

In woodwork the pressure of the nut is apt to compress the wood, causing the bolt head and nut to sink into the wood, and to obviate this, anchor plates are used to increase the area receiving the pressure; thus in Fig. 384 a plate is tapped to serve instead of a nut, and a similar plate may of course be placed under the bolt head.

The Franklin Institute or United States Standard for the dimensions of bolt heads and nuts is as follows. In Fig. 385, D represents the diameter of the bolt, J represents the short diameter or width across flats of the bolt head or of the nut, being equal to one and a half times the diameter of the bolt, plus 1/16 inch for finished heads or nuts, and plus 1/8 inch for rough or unfinished heads or nuts. K represents the depth or thickness of the head or nut, which in finished heads or nuts equals the diameter of the bolt minus 1/16 inch, and in rough heads equals one half the distance between the parallel sides of the head, or in other words one half the width across the flats of the head.

H represents the thickness or depth of the nut, which for finished nuts is made equal to the diameter of the bolt less 1/16 inch, and therefore the same thickness as the finished bolt head, while for rough or unfinished nuts it is made equal to the diameter of the bolt or the same as the rough bolt head. I represents the long diameter or diameter across corners, which, however, is a dimension not used to work to, and is inserted in the following tables merely for reference:--

TABLE OF THE FRANKLIN INSTITUTE STANDARD DIMENSIONS FOR THE HEADS OF BOLTS AND FOR THEIR NUTS, WHEN BOTH HEADS AND NUTS ARE OF HEXAGON FORM, AND ARE POLISHED OR FINISHED.

+------------+-------------+-----------+---------------+-----------+ | Diameter | Diameter at | Number of | Diameter | Thickness | | at top | bottom of | Threads | across Flats, | or | | of Thread. | Thread. | per inch. | or short | Depth. | | | | | diameter. | | +------------+-------------+-----------+---------------+-----------+ | 1/4 | .185 | 20 | 7/16 | 3/16 | | 5/16 | .240 | 18 | 17/32 | 1/4 | | 3/8 | .294 | 16 | 5/8 | 5/16 | | 7/16 | .345 | 14 | 23/32 | 3/8 | | 1/2 | .400 | 13 | 13/16 | 7/16 | | 9/16 | .454 | 12 | 29/32 | 1/2 | | 5/8 | .507 | 11 | 1 | 9/16 | | 3/4 | .620 | 10 | 1-3/16 | 11/16 | | 7/8 | .731 | 9 | 1-3/8 | 13/16 | | 1 | .837 | 8 | 1-9/16 | 15/16 | | 1-1/8 | .940 | 7 | 1-3/4 | 1-1/16 | | 1-1/4 | 1.065 | 7 | 1-15/16 | 1-3/16 | | 1-3/8 | 1.160 | 6 | 2-1/8 | 1-5/16 | | 1-1/2 | 1.284 | 6 | 2-5/16 | 1-7/16 | | 1-5/8 | 1.389 | 5-1/2 | 2-1/2 | 1-9/16 | | 1-3/4 | 1.491 | 5 | 2-11/16 | 1-11/16 | | 1-7/8 | 1.616 | 5 | 2-7/8 | 1-13/16 | | 2 | 1.712 | 4-1/2 | 3-1/16 | 1-15/16 | | 2-1/4 | 1.962 | 4-1/2 | 3-7/16 | 2-3/16 | | 2-1/2 | 2.176 | 4 | 3-13/16 | 2-7/16 | | 2-3/4 | 2.426 | 4 | 4-3/16 | 2-11/16 | | 3 | 2.629 | 3-1/2 | 4-9/16 | 2-15/16 | | 3-1/4 | 2.879 | 3-1/2 | 4-15/16 | 3-3/16 | | 3-1/2 | 3.100 | 3-1/4 | 5-5/16 | 3-7/16 | | 3-3/4 | 3.377 | 3 | 5-11/16 | 3-13/16 | | 4 | 3.567 | 3 | 6-1/16 | 3-15/16 | | 4-1/4 | 3.798 | 2-7/8 | 6-7/16 | 4-3/16 | | 4-1/2 | 4.028 | 2-7/8 | 6-13/16 | 4-7/16 | | 4-3/4 | 4.256 | 2-5/8 | 7-3/16 | 4-11/16 | | 5 | 4.480 | 2-1/2 | 7-9/16 | 4-15/16 | | 5-1/4 | 4.730 | 2-1/2 | 7-15/16 | 5-3/16 | | 5-1/2 | 4.953 | 2-3/8 | 8-5/16 | 5-7/16 | | 5-3/4 | 5.203 | 2-3/8 | 8-11/16 | 5-11/16 | | 6 | 5.423 | 2-1/4 | 9-1/16 | 5-15/16 | +------------+-------------+-----------+---------------+-----------+

Note that square heads are supposed to be always unfinished, hence there is no standard for their sizes if finished.

The Franklin Institute standard dimensions for hexagon and square bolt heads and nuts when the same are left unfinished or rough, as forged, are as follows:--

+----------+-------------+-------------+---------------+-----------+ | | Diameter | Diameter | Short | Thickness | | Bolt | across | across | diameter, | or | | Diameter | corners, or | corners or | or diameter | depth for | | in | long | long | across flats | square or | | Inches. | diameter of | diameter of | for square or | hexagon | | | hexagon | square | hexagon heads | heads. | | | heads. | heads. | and nuts. | | +----------+-------------+-------------+---------------+-----------+ | | Inch. | Inch. | Inch. | Inch. | | 1/4 | 37/64 | 7/10 | 1/2 | 1/4 | | 5/16 | 11/16 | 10/12 | 19/32 | 19/64 | | 3/8 | 51/64 | 63/64 | 11/16 | 11/32 | | 7/16 | 9/10 | 1-7/64 | 25/32 | 25/64 | | 1/2 | 1 | 1-15/64 | 7/8 | 7/16 | | 9/16 | 1-1/8 | 1-23/64 | 31/32 | 31/64 | | 5/8 | 1-7/32 | 1-1/2 | 1-1/16 | 17/32 | | 3/4 | 1-7/16 | 1-49/64 | 1-1/4 | 5/8 | | 7/8 | 1-21/32 | 2-1/32 | 1-7/16 | 23/32 | | 1 | 1-7/8 | 2-19/64 | 1-5/8 | 13/16 | | 1-1/8 | 2-2/32 | 2-9/16 | 1-13/16 | 29/32 | | 1-1/4 | 2-5/16 | 2-53/64 | 2 | 1 | | 1-3/8 | 2-17/32 | 3-3/32 | 2-3/16 | 1-3/32 | | 1-1/2 | 2-3/4 | 3-23/64 | 2-3/8 | 1-3/16 | | 1-5/8 | 2-31/32 | 3-5/8 | 2-9/16 | 1-9/32 | | 1-3/4 | 3-3/16 | 3-57/64 | 2-3/4 | 1-3/8 | | 1-7/8 | 3-13/32 | 4-5/32 | 2-15/16 | 1-15/32 | | 2 | 3-5/8 | 4-27/64 | 3-1/8 | 1-9/16 | | 2-1/4 | 4-1/16 | 4-61/64 | 3-1/2 | 1-3/4 | | 2-1/2 | 4-1/2 | 5-31/64 | 3-7/8 | 1-15/16 | | 2-3/4 | 4-29/32 | 6 | 4-1/4 | 2-1/8 | | 3 | 5-3/8 | 6-17/32 | 4-5/8 | 2-5/16 | | 3-1/4 | 5-13/16 | 7-1/16 | 5 | 2-1/2 | | 3-1/2 | 6-7/64 | 7-39/64 | 5-3/8 | 2-11/16 | | 3-3/4 | 6-21/32 | 8-1/8 | 5-3/4 | 2-7/8 | | 4 | 7-3/32 | 8-41/64 | 6-1/8 | 3-1/16 | | 4-1/4 | 7-9/16 | 9-3/16 | 6-1/2 | 3-1/4 | | 4-1/2 | 7-31/32 | 9-3/4 | 6-7/8 | 3-7/16 | | 4-3/4 | 8-13/32 | 10-1/4 | 7-1/4 | 3-5/8 | | 5 | 8-27/32 | 10-49/64 | 7-5/8 | 3-13/16 | | 5-1/4 | 9-9/32 | 11-23/64 | 8 | 4 | | 5-1/2 | 9-23/32 | 11-7/8 | 8-3/8 | 4-3/16 | | 5-3/4 | 10-5/32 | 12-3/8 | 8-3/4 | 4-3/8 | | 6 | 10-19/32 | 12-15/16 | 9-1/8 | 4-9/16 | +----------+-------------+-------------+---------------+-----------+

The depth or thickness of both the hexagon and square nuts when left rough or unfinished is, according to the above standard, equal to the diameter of the bolt.

The following are the sizes of finished bolts and nuts according to the present Whitworth Standard. The exact sizes are given in decimals, and the nearest approximate sizes in sixty-fourths of an inch:--

+-------------+------------------------+----------------------+ | Diameter of | Width of nuts across | Height of bolt | | bolts. | flats. | heads. | +-------------+----------+-------------+--------+-------------+ | 1/8 | .338 | 21/64 _f_ | .1093 | 7/64 | | 3/16 | .448 | 29/64 _b_ | .1640 | 5/32 | | 1/4 | .525 | 33/64 _f_ | .2187 | 7/32 | | 5/16 | .6014 | 19/32 _f_ | .2734 | 17/64 | | 3/8 | .7094 | 45/64 _f_ | .3281 | 21/64 | | 7/16 | .8204 | 53/64 _b_ | .3828 | 3/8 _f_ | | 1/2 | .9191 | 29/32 _b_ | .4375 | 7/16 | | 9/16 | 1.011 | 1-1/64 _b_ | .4921 | 31/64 _f_ | | 5/8 | 1.101 | 1-3/32 _f_ | .5468 | 35/64 | | 11/16 | 1.2011 | 1-13/64 _b_ | .6015 | 19/32 _f_ | | 3/4 | 1.3012 | 1-19/64 _f_ | .6562 | 21/32 | | 13/16 | 1.39 | 1-25/64 _b_ | .7109 | 45/64 _f_ | | 7/8 | 1.4788 | 1-31/64 _b_ | .7656 | 49/64 | | 15/16 | 1.5745 | 1-37/64 _b_ | .8203 | 13/16 _f_ | | 1 | 1.6701 | 1-43/64 _b_ | .875 | 7/8 | | 1-1/8 | 1.8605 | 1-55/64 _f_ | .9843 | 63/64 | | 1-1/4 | 2.0483 | 2-3/64 _f_ | 1.0937 | 1-3/32 | | 1-3/8 | 2.2146 | 2-7/32 _b_ | 1.2031 | 1-13/64 | | 1-1/2 | 2.4134 | 2-13/32 _f_ | 1.3125 | 1-5/16 | | 1-5/8 | 2.5763 | 2-37/64 _b_ | 1.4128 | 1-27/64 | | 1-3/4 | 2.7578 | 2-3/4 _f_ | 1.5312 | 1-17/32 | | 1-7/8 | 3.0183 | 3-1/16 _f_ | 1.6406 | 1-41/64 | | 2 | 3.1491 | 3-5/32 _b_ | 1.75 | 1-3/4 | | 2-1/8 | 3.337 | 3-11/32 _b_ | 1.8523 | 1-55/64 | | 2-1/4 | 3.546 | 3-35/64 _b_ | 1.9687 | 1-31/32 | | 2-3/8 | 3.75 | 3-3/4 | 2.0781 | 2-5/64 | | 2-1/2 | 3.894 | 3-57/64 _f_ | 2.1875 | 2-3/16 | | 2-5/8 | 4.049 | 4-3/64 _f_ | 2.2968 | 2-19/64 | | 2-3/4 | 4.181 | 4-3/16 _b_ | 2.4062 | 2-13/32 | | 2-7/8 | 4.3456 | 4-11/32 _f_ | 2.5156 | 2-33/64 | | 3 | 4.531 | 4-17/32 _b_ | 2.625 | 2-5/8 | +-------------+----------+-------------+--------+-------------+

The thickness of the nuts is in every case the same as the diameter of the bolts: _f_ = full, _b_ = bare.

When bolts screw directly into the work instead of passing through it and receiving a nut, they come under the head of either tap bolts, set screws, cap screws, or machine screws. A tap bolt is one in which the full length of the stem or body is threaded, and differs from a set screw, which is similarly threaded, in the respect that in a set screw the head is square and its diameter is the same as the square bar of steel or iron (as the case may be) from which the screw was made, while in the tap bolt the head is larger in diameter than the bar it was made from. Furthermore a tap bolt may have a hexagon head, which is usually left unfinished unless ordered to be finished, as is also the case with set screws.

Cap screws are made with heads either hexagon, square, or round, and also with a square head and round collar, as in Fig. 386, the square heads being of larger diameter than the iron from which they were made. When the heads of cap screws are finished they are designated as "milled heads."

A machine screw is a small screw, such as in Fig. 387, the diameter of the body being made to the Birmingham wire gauge, the heads being formed by upsetting the wire of which they are made. They have saw slots S for a screw driver, the threads having special pitches, which are given hereafter. The forms of the heads are as in Fig. 387, A being termed a Fillister, B a countersink, and C a round head. The difference between a Fillister head of a machine screw and the same form of head in a cap screw is that the former is upset cold, and the latter is either forged or cut out of the solid metal.

When the end of a screw abuts against the work to secure it, it is termed a set screw. The ordinary form of set screw is shown in Fig. 389, the head being square and either black or polished as may be required. The ends of the set screws of commerce, that is to say, that are kept on sale, are usually either pointed as at A, Fig. 388, slightly bevelled as at B, or cupped as at D. If left flat or only slightly bevelled as at B, they are liable, if of steel and not hardened, or if of iron and case-hardened only, to bulge out as at C. This prevents them from slacking back easily or prevents removal if necessary, and even though of hardened steel they do not grip very firmly. On this account their points are sometimes made conical, as at A. This form, however, possesses a disadvantage when applied to a piece of work that requires accurate adjustment for position, inasmuch as it makes a conical indentation in the work, and unless the point be moved sufficiently to clear this indentation the point will fall back into it; hence the conical point is not desirable when the piece may require temporary fixture to find the adjustment before being finally screwed home. For these reasons the best form of set screw end is shown at D, the outside of the end being chamfered off and the inside being cupped, as denoted by the dotted lines. This form cuts a ring in the work, but will hold sufficiently for purposes of adjustment without being screwed home firmly.

In some cases the end of the set screw is tapped through the enveloping piece (as a hub) and its end projects into a plain hole in the internal piece of the work, and in this case the end of the thread is turned off for a distance of two or three threads, as at A in Fig. 390. Similarly, when the head of the screw is to act or bear upon the work, the thread may be turned off as at B in the figure.

When a bolt has no head, but is intended to screw into the work at one end, and receive a nut at the other, it is termed a stud or standing bolt. The simplest form of standing bolt is that in which it is parallel from end to end with a thread at each end, and an unthreaded part in the middle, but since standing bolts or studs require to remain fixed in the work, it is necessary to screw them tightly into their places, and therefore firmly home. This induces the difficulty that some studs may screw a trifle farther into the work than others, so that some of the stud ends may project farther through the nuts than others, giving an appearance that the studs have been made of different lengths. The causes of this may be slight variations in the tapping of the holes and the threading of the studs. If those that appear longest are taken out and reduced to the lengths of the others, it will be found sometimes that the stud on the second insertion will pass farther into the work than at the first, and the stud will project less through the nut than the others. To avoid this those protruding most may be worked backward and forward with the wrench and thus induced to screw home to the required distance, but it is better to provide to the stud a shoulder against which it may screw firmly home; thus in Fig. 391 is a stud, whose end A is to screw into the work, part B is to enter the hole in the work (the thread in the hole being cut away at the mouth to receive B). In this case the shoulder between B and C screwing firmly against the face of the work, all the studs being made of equal length from this shoulder to end E, then the thickness of the flange or work secured by the nut being equal, the nuts will pass an equal distance on end D, and E will project equally through all the nuts. The length of the plain