It is believed that with the present screw machine practice in shops of to-day these small parts can readily be turned out accurately and cheaply in large quantities. The nuts and guards made in any one shop must be exactly of standard dimensions, so that the product of different periods will be interchangeable.
The taper should be about one inch to one foot. With this taper the nut can be readily turned in or out, but there is friction enough to hold the guard and nut together even if the spring is off.
In [Fig. 10], the top of the guard is recessed in the form of a hollow inverted pyramid of six sides, to correspond to a hexagonal nut. The angle of two opposite sides of this recess, which should be about 75 degrees, will both surely lock the nut and still permit of its being turned with a wrench.
The guard is kept from turning by slabbing off the stem, in the same manner as described and shown in [Fig. 9].
To facilitate the removal of the nut, the edges should be slightly chamfered. An unfinished nut simply drilled and tapped is all that is desired. Any hexagonal or square nut within the size of the tapered recess will be locked.
With this construction, the nut cannot turn in either direction without compressing the spring and is therefore locked, and, in the event of the spring breaking or being left off, the nut is well protected in its recess from the possible turning effects of water currents, and experiments have shown that it will still stay in place.
With machine molding it will be possible to make these guards complete in foundry, requiring no machine work further than a possible broaching out of hole to fit the stem, as a fairly good fit is necessary.
While both of these devices are effective even though not tightened down to a shoulder, they should be so tightened for greater safety and to fix the lift at the half-inch limit.
39. Pipe Sizes.
a. Water and steam pipe connections must have standard flanges to connect with pipes of the sizes given below.