... The inner mold comprises a steel shell E curved to the form of the inside of the conduit; inside this steel shell is a reinforcing lagging, and at each end there is a wooden diaphragm F. Passing through both end diaphragms and having its ends flush with the end planes of the mold is a timber G. Rearward projecting lips e are secured to the lagging at the rear end of the mold and on each side of the timber G. The diaphragms F have each two arms f which project horizontally beyond the surface of the inner mold and engage the tracks D; locking dogs H are pivoted to the arms f so as to hook ... — Concrete Construction - Methods and Costs • Halbert P. Gillette
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