Fig. 392.
If it be left slightly larger than d, but the depth of the thread less than a, then it may be held sufficiently firmly by the fit of the threads (without the aid of screwing against a shoulder) to prevent unscrewing when releasing the nut, and may be screwed within the work until its end projects the required distance; thus all the studs may project an equal distance, but there will be the disadvantage that when the studs require removing and are corroded the plain part is apt to twist off, leaving the end a plugging the hole. The plain part c may be left of same diameter as a, both being larger than d; but in this case the difficulty of having all the studs project equally when screwed home, as previously mentioned, is induced; hence c may be larger than a, and a shoulder left at b, as in the figure; this would afford excellent facility for unscrewing the stud to remove it, as well as insuring equal projection of e. The best method of all is, so far as quality goes, to make the plain part c square, as in [Fig. 392], which is an English practice, the square affording a shoulder to screw up against and secure an equal projection while serving to receive a wrench to put in or remove the stud. In this case the holes in the flange or piece bolted up being squared, the stud cannot in any case unscrew with the nut. The objection to this squared stud is that the studs cannot be made from round bar iron, and are therefore not so easily made, and that the squaring of the holes in the flange or part of the work supported by the stud is again extra work, and for these reasons studs with square instead of cylindrical mid-sections have not found favor in the United States.
Fig. 393.
An excellent method of preventing the stud from unscrewing with the nut is to make the end a longer than the nut end, as in [Fig. 393], so that its threads will have more friction; and this has the further advantage that in cast iron it serves also to make the strength of the thread equal to that of the stud. As the faces of the nuts are apt when screwed home to score or mark the face of the work, it adds to the neatness of the appearance to use a washer w beneath the nut, which distributes the pressure over a greater area of work surface.
In some practice the ends a of studs are threaded taper, which insures that they shall fit tight and enables their more easy extraction.
Fig. 394.