less than a one-half (1/2) inch space between them, in order to facilitate painting. The various members attached to any pin must be packed as closely as practicable, and all interior vacant spaces must be filled with steel fillers, where their omission would permit of motion of any member on the pin. All bars are to lie in planes as nearly as possible parallel to the central truss-plane, no divergence exceeding one eighth (1/8) of an inch to the foot being permitted.

In detailing I struts composed of four angles with a single line of lacing, the clear distance between backs of angles shall never be made less than three-quarters (3/4) of an inch, in order to permit the insertion of a small paint-brush.

The greatest allowable pressure upon expansion-rollers of fixed spans, when impact is considered, shall be determined by the equation

p = 600d

where p is the permissible pressure in pounds per lineal inch of roller, and d is the diameter of the latter in inches. The least allowable diameter for expansion-rollers is three (3) inches.

Rollers shall be enclosed in boxes made practically dust-tight, and filled with an oil that will not congeal under any possible temperature. These boxes must be so designed as to permit of a free movement of the rollers in the longitudinal direction of span sufficient to take up the extreme variations in length due to temperature changes and deflection, and at the same time prevent any transverse motion of the end of the span.

All shoe-plates, bed-plates, and roller-plates are to be so stiffened that the extreme fibre-stress under bending, when impact is included, shall not exceed sixteen thousand (16,000) pounds.

Pedestals shall be either of cast steel or built up of plates and shapes. In built pedestals, all bearing surfaces of the base-plates and vertical bearing-plates must be planed. The vertical plates must be secured to the base by angles having at  least  two  rows  of  rivets in  the  vertical legs;  and  the  said