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).
Blueprint comparing 4 inch and 7 inch stroke designs with associated measurements.
| Identifier | ExFiles\Box 170\2\ img024 | |
| Date | 7th May 1931 | |
| 1650 7 1/2 ARM. 640# = 1" OG - Special To off Identum, 4" STROKE 300 250 200 150 100 57 7" STROKE 250 200 150 100 60 32 30 D.Faraday 7.5.31 | ||