The following formulae shall be used in proportioning rollers:

For greatest total loads, including impact, with draw at rest,

p = 600d

for loads with draw in motion,

p = 200d

where p is the permissible pressure in pounds per lineal inch of roller, and d is its mean diameter in inches.

In no case shall the roller be less than twelve (12) inches in diameter and seven (7) inches on face.

All rollers, and the faces of the upper and lower tracks which are in contact with the rollers, are to be turned smooth to the forms of right frustums of cones, the vertices of which intersect at the centre of the drum, so that the rollers will have perfect contact with the tracks throughout their travel around the entire circumference.

A bearing is to be turned in the centre of each roller for the radial rod, and oil-holes are to be provided on both the interior and the exterior ends of the rollers, so that these bearings can be kept well lubricated.

The outer ends of the radial rods are to pass through the rollers, and the inner ends are to attach to a circular plate fitting closely around the centre casting. These radial rods are to be provided with either turnbuckles or nuts for adjusting the position of the rollers. Only square sections are to be used for the rods, and each must contain at least one square inch of section. The end of the rod passing through the roller must be upset so as to provide a turned shaft for the latter at least one and one-half (1 1/2) inches in diameter. The outer ends of these rods are to pass through a stiff steel ring of rolled or built channel section, which is to serve as a spacer for the rollers. These channels must be made wide, but not deep, and their section is to be commensurate with the size of the turntable. They are to be held away from the rollers by friction-washers on the rods.

On the inside of the rollers collars are to be forged and