Page:Miscellaneous Papers on Mechanical Subjects.djvu/38

 30 the different characters of thread, and more particularly with the depth. The centre part not being liable to wear while the thread is subject to friction and accidental injury, the original proportion of strength ought to be considerably in favour of the thread.

Such being the variety and vagueness of the principles avowed in the subject, a corresponding latitude might naturally be expected in their practical application, and accordingly we find, instead of that uniformity which is so desirable, a diversity so great as almost to discourage any hope of its removal. The only mode in which this could be attempted with any probability of success would be by a sort of compromise, all parties consenting to adopt a medium for the sake of common advantage. The average pitch and depth of the various threads used by the leading engineers would thus become the common standard; which would not only have the advantage of conciliating general concurrence, but would, in all probability, be nearer the true standard for practical purposes than any other.

Messrs. Whitworth and Company were led, some years ago, to alter the threads of their screws on this principle, in consequence of various objections urged against those they had previously adopted, and the result of the experiment has been abundantly satisfactory.