1. J. Churchward, US Patent No. 1,377,543 (1920).
2. D.J. Kotechi, V.B. Rajan, Weld. Res. Suppl. (July 1998) 293–298.
3. Roll Crusher Maintenance, Rebuilding, and Repair, Pit and Quarry, October 1970, pp. 104–106.
4. E. Taylor, Private Communication, Canadian Pacific Railway, 1981.