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 dimensions and weights for various 40/50 HP size, Group A starter motors.
| Identifier | ExFiles\Box 61b\3\ scan0112 | |
| Date | 3rd March 1921 guessed | |
| Y503 - 6027 X.543. STARTER MOTOR TABLES. 40/50 HP. size. GROUP A.{Mr Adams} MOTOR. X.3247 C.A.V. ZC. X.3161 Lucas A.510. X.1058 Bijur A.21. X.1248 Bosch S.45. X.2642 RR.17. (CLC) X.2642 RR.24 (CLC) DIMENSIONS. Carcase diameter. 4.500 5.650 5.500 5.900 Not circular Not circular Carcase length. 5.375 3.750 7.600 4.760 Carcase thickness. .280 .375 .275 .385 Armature diameter. 2.870 3.575 3.560 3.700 3.600 3.600 Armature active length. 2.800 2.050 3.000 2.870 2.550 2.550 Driving end arm: overhang. (") .9" .85" 1.0" .9" 1.3" .95" Length of comm. conns. excluding comm. spokes. (") 1.45 1.0 1.05 .9 1.25 1.2 Ditto, including comm. spokes. (") 1.7 1.2 1.3 1.05 1.5 1.45 Ratio armature dia. to carcase dia. .64 .63 .65 .63 — — WEIGHTS (lbs) Complete machine but without pinion sprocket or suspension. 19.0 21.4 30.5 39.15 35.0 34.5 Arm: without pinion or sprocket. 6.94 7.66 11.25 11.0 11.06 10.62 Carcase & pole pieces bare. — — — — 13.69 13.69 Armature stampings — — — — — — -1- | ||