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).
Photographic print showing a top-down view of seven spark plugs in a row.
| Identifier | ExFiles\Box 58\2\ Scan046 | |
| Date | 1st July 1932 guessed | |
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