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).
Comparison table of features for various horsepower dynamos and motors.
| Identifier | ExFiles\Box 165\6\ img044 | |
| Date | 16th December 1926 | |
| L.X5660 E.F.C 16.12.26. DYNAMOS. MOTORS. | | 20 HP. | 40/50 HP. | 20 HP. | 40/50 HP. | Sequence. Pole Pieces. | Laminated. | Solid. | Laminated. | Laminated. | Solid. Armature laminations. | Thin, mica insulated & milled. | Thick, mica insulated & milled. | Thin, mica insulated & milled. | Thin, mica insulated & milled. | Thick, mica insulated & milled. Slots. | Skewed. | Skewed. | Straight. | Straight. | Straight. EFC. | ||