sixteenths (3 7/16) inches net in diameter. The play between rollers and their pins shall not be over one thirty-second (1/32) of an inch. The links forming the support for the ends of trusses are to be proportioned by the formula

where p = intensity of working compressive stress, l = greatest unsupported length of one link, and t = thickness of same.

In all drawbridges where, on account of infrequent operation combined with great changes in temperature and great length of arms, there is a tendency to drag the rollers longitudinally on their hearings, the detailing of the link supports must be such as to provide sufficient rigidity to overcome the friction of the rollers on their bearings, and thus permit the lifting apparatus to accommodate itself to extreme changes of temperature without overstraining any of its parts.

The bearings for rollers on the shoes shall be cupped one-eighth (1/8) inch or more in depth so as to provide ample bearing area, using an intensity of ten thousand (10,000) pounds, impact being included in the calculated load. The shoes to receive the end rollers may be made of either cast or structural steel, and are to be anchored firmly to the masonry, The two shoes at one end of span are to be connected to each other by means of adjustable rods not less than one and one-half (1 1/2) Inches in diameter, and strong enough to take up the entire thrust from the toggle.

Shimming-plates varying in thickness from one fourth (1/4) to one half (1/2) of an inch and of a total depth of not less than three (3) inches are to be used beneath the shoes so as to provide adjustment for the ends of the span.

Shoulders must be provided on the shoes to furnish a bearing for the rollers when they are lowered by the toggle. Each shoulder must be turned so as to fit the roller exactly, when the axis of the pin through the said roller is in the vertical plane of the truss. The height of these shoulders above  the  bottom  of  the rollers shall be about one third of  the diameter