The three types of leveling rods used by American engineers were all sliding rods.  The rods were formed of two strips of wood, each three-fourths of an inch by one and three-fourths inches by six and one-half feet long, connected by two metal sleeves, with one or both having a clamping screw, for fixing the rod into position when the two parts are separated or extended beyond six feet six inches.  The Philadelphia Rod is divided to tenths, and reads to two hundredths of a foot.  The Boston and New York were divided into hundredths of a foot and reading by verniers to thousandths.

The rod most commonly used was the Philadelphia rod.  The Boston rod was very convenient to use because of its lightness, but the parts were made too frail to endure the rough usage of this country, and, therefore, American engineers have generally given the preference to another, made heavier and more substantial.  The New York rod was very similar in construction to the Philadelphia and differed primarily in its graduations and number of clamping screws.

Source:  "A Manual of the Principal Instruments Used in American Engineering and Surveying, Manufactured by W. & L. E. Gurley, Troy, N.Y.," Twenty-First Edition, 1874, pp. 133-136.