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).
Photograph of a broken two-piece spark plug.
| Identifier | ExFiles\Box 162\5\ img097 | |
| Date | 23th January 1939 guessed | |
| SG{Arthur F. Sidgreaves - MD} A | ||