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 for Tungsten used in high and low tension points from various suppliers.
| Identifier | ExFiles\Box 35\5\ scan 089 | |
| Date | 19th January 1920 | |
| TUNGSTEN FOR HIGH AND LOW TENSION POINTS Ref. Letter. | Firm. | Contacts or rods. | Description. | Remarks. A | L.P.S. | C | L.T. contacts for Watford Magnetos. | Fitted (First lot unsatisfactory EH1/AT 30417. (Second " lost. (Third lot B | Gallen-Kamp. | R(.125" dia) | L.T. contacts for R.R. battery ignition. | Expl. Shop unable to work. C | Delco. | C | Delco contacts obtained from Remy Elec. Co. | Fitted to screw and blade of R.R. Battery Ignition. Unsatisfactory owing to bad condenser connection. Running on 10,000 mile car (2 EX) D | B.T.H. | R (.125" dia) | L.T. contacts for R.R. battery ignition. | Expl. Shop unable to work. E | Ind. Lamp & Wire Co. | C | for Bosch magneto. | F | " | C | Delco. | G | " | C (.070" dia) | | H | " | C (.125" dia.) | For L.T. contacts. | Fitted to blade and screw of battery ignition - Run 6 hours on bench. O.K. fitted to 49 GB. I | " | R (.109" dia.) | | | ||