A screw-stud is a cylindrical piece of metal screwed at one or both ends, and intended to be fixed in a flange, rim, or other portion. A stud having a screw at only one end is provided with a small pin-hole at that end which has no screw, the hole being required to contain a taper pin similar to those treated in the previous section. A stud with a screw at each end, is provided with a screw-nut at one end, the opposite end being that which is to be fixed in the flange or other portion. All the studs here treated are such as those employed for connecting cylinder-lids to their cylinders, and for connecting a great number of flanges of several classes. It may be here generally stated that studs are a class of substitutes for bolts, and are never used except in places that will not admit headed bolts. Studs should never be made of steel unless they are to be screwed with a lathe.

Studs that are intended to tightly connect two flanges together, are of two sorts, each of a distinct shape. One of these is that of a piece which is screwed along its entire length, and the other is that of a piece having a thread at each end, and a cylindrical or plain part in between. Those that consist entirely of screws, are denoted by Fig. 930, and those having plain mid-parts are denoted by Fig. 929. Either of these sorts may be used for any one purpose; but those which have plain portions are superior to the others, although those that are entirely screwed are quicker made. The forming of the two varieties must be separately described.

Screw-studs which are to be without any plain part, are made in lots of four, six, or eight, of one diameter, and at one time. A piece of wire or rod is prepared of sufficient length to make six, eight, or whatever number may be convenient, and it is screwed along its entire length, excepting an inch or two at one end, which is square, and smaller than the remainder, the square end constituting a holder or head by which the piece is held during screwing. A long stud-piece of this class is shown by Fig. 931, being screwed alon its whole length and ready to be cut into studs of proper length. Studs thus made are screwed with dies, and if not exceeding five-eighths or three-quarters of an inch in diameter, the stud-piece can be gripped with the square head in a bench-vice and screwed with a pair of dies in an ordinary die-frame. Comparative large stud-pieces of this class that maybe an inch or more in diameter, are screwed with machine-dies. As soon as a long piece has been screwed to the exact diameter desired along its length, it can be cut into pieces of a proper length for use, by means of sawing.

The mode of thus making a number of studs together in one piece, is a rapid method Of formation only suited to small studs. Dies will not form the threads of such pieces properly if they are more than an inch in diameter; and some dies will not properly screw a piece if it is more than three-quarters in diameter, or of greater length than five or six inches. The characters and modes of making dies are described in the chapter on tool-making.

In order to accurately screw a stud-piece, care must be exercised to make the screw as nearly parallel as possible along its whole length; and if the diameter is that desired, any part of the piece can be used for a stud. But it will be discovered that most of the pieces thus made are smaller in diameter at their mid-parts than at the ends; so that when the studs are produced by sawing off, those that are too small must be rejected. The gauge-nut or measuring-nut, used during the screwing, should have its screw a little larger in diameter than the diameter of the intended studs, and the piece is to be screwed to tightly fit this nut; consequently, a small portion of metal will remain for reducing the thread to the finished diameter. This small quantity can now be pared off with a good die-nut which has been properly formed for its use; with this the studs can be finally adjusted to the diameter with but little trouble.

Another mode of screwing several pieces to one precise diameter, consists in fixing packing pieces of proper thickness between the two dies in their frame; in order that while a piece is being screwed, the operator may know it to be reduced to the proper diameter by the time the dies are advanced tight against the packing-pieces, after which they cannot be brought nearer to each other, and, therefore, cannot make the screw any smaller. Stud-pieces are also accurately formed by means of lathe-screwing, by which the required parallelism is easily obtained, and the thread properly shaped.

It is now needful to mention the making of studs having plain mid-portions. These should be made singly, each one being cut to the finished length at the time of forging, with only an additional sixteenth of an inch at each end, when it may be specially necessary to finish them in the lathe to the precise shape. After forging, each lot require to be turned and screwed ; and the particular lathe selected for any one lot, is suited to their diameters, because small ones not more than three-quarters of an inch in diameter can be screwed by hand-screwing; whereas larger ones require to be screwed with wheels. By means of lathe-turning and screwing, studs of three inches in diameter or any larger size, can be perfectly and accurately made, which cannot be done with dies.

When several hundred studs are required at one time, their turning is executed in one lathe, and their screwing in another. By this mode, one lathe can be kept turning them to their exact diameters by means of gap-gauges, while another lathe is appropriated entirely to their screwing. This will avoid shifting a variety of apparatus for the purpose of putting a lathe into order for screwing; and will also allow studs to be centred and turned with a lathe which is entirely without screwing apparatus.

If studs are to be screwed by hand, it is proper to commence the screwing of every one with the wheels, whether it is to be finished with a hand screw-tool, or with a slide-rest tool. The quickest mode of smoothly finishing the thread is by hand-screwing, whether the studs are small or large. But the amount of wheel-screwing which small studs require is very little compared with that required for large ones. If the stud is only three-eighths or half an inch in diameter, the wheel-screwing should consist in merely making a thread-groove by only one advance of the tool along the stud; after which, the hand-screwing is a preferable and rapid process for removing the remaining metal. Small studs should therefore be principally screwed by hand, and large ones by wheels. Those that may be an inch or more in diameter, should be screwed with wheels until near their ultimate diameter, after which it is proper to smooth them with a hand screw-tool, that they may accurately fit their respective gauge-nuts, and also be smoothly finished. All hand-screwing of this character constitute processes which are distinct from wheel-screwing; therefore, if the same lathe is required to both commence and finish the screwing, all the studs require to be first screwed with the wheels, previous to finishing any one of them by hand.

Studs are also forged singly with handles. A stud thus made is furnished with a small square handle which is produced at one end by thinning the metal; consequently, the square part of a stud is similar to that of a long stud-piece to be cut into proper lengths. Studs having handles are denoted by Figs. 932, 933, and 934. Such can be very conveniently held while being turned and screwed in a lathe, and also while in a bench-vice, or in a screwing-machine.