- A short length of circular glass tubing, of inside diameter large enough to contain a compass needle, stands with its axis vertical and has single or multiple loops of wire wound on it in vertical diametral planes. - "The Earliest Electromagnetic Instruments", Robert A. Chipman.
- First, by their diameters at the pitch circle or pitch diameter and the number of teeth they contain; second, by the number of teeth in the wheel and the pitch of the teeth; and third, by a system known as diametral pitch. - "Modern Machine-Shop Practice, Volumes I and II", Joshua Rose.
- What is the diametral pitch? - "Modern Machine-Shop Practice, Volumes I and II", Joshua Rose.