From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Laboratory report with photomicrographs comparing the surface structure of an American spring and a Firth's spring.
| Identifier | ExFiles\Box 154a\4\ scan0065 | |
| Date | 15th February 1938 guessed | |
| ROLLS-ROYCE LABORATORY REPORT: M.1486/8 x 250 Upper surface of American spring after removing .002" depth of material. M.1486/9 x 250 Firth's spring No.2. after removing the whole of the decarburised surface layer to reveal normal structure beneath. | ||