The main tubes for the 455 feet spans use a tubular strut of elliptical cross-section; 16 feet 9 inches in width and 12 feet 3 inches in depth. Brereton quotes a total length of each tube of 461 feet. They are fabricated from 1/2, 5/8 and 3/4 inch thick wrought iron plates, generally 10 feet long x 2 feet wide, rolled and joggled as necessary and rivetted together. At the longitudinal joints the plates are lapped but the transverse joints incorporate double-covered butt joints; 3/4, 1 and 1 1/4 inch diameter rivets being used, according to position. An important feature to note is that between each vertical hanger or chain connection the tubes are straight.

Extending throughout the length of both tubes are sets of internal stiffeners, formed from 12 x 1/2 inch plates set on edge, three at the top and three at the bottom. Spaced at about 20 feet centres within the length of each tube are annular stiffeners, 15 inches deep with 2 1/2 x 5/8 inch edge angles, additionally reinforced by two single vertical angles 2 1/2 x 3/8 inch and a double vertical angle on the centre line.

The ends of the tubes incorporate closed diaphrams, while 2 inch diameter solid iron cross ties provided additional lateral stiffening, their number increasing towards the ends. To ventilate the interiors, a number of 2 inch diameter holes were drilled in the undersides, thus mitigating the damaging affect arising from the onset of any condensation.