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).
List of specifications for a commutator and brushes.
| Identifier | ExFiles\Box 61b\3\ scan0111 | |
| Date | 24th January 1929 guessed | |
| -3- Contd. F.{Mr Friese} Commutator and brushes. (a) Commutator diameter. (b) Commutator length. (g) Grade and hardness of brushes. (d) Number of brushes. (e) Arrangement of brushes. (f) Brush contact total area for current. (g) Advance or retard of brushes. EFC. | ||