1941s used AC 104s as well as M8s.
Under group 2.270 in my 1929-1950 Chevrolet parts book is shown, in part, the following 1941-48:
All...No. 104 (10 MM) Standard equip. on trucks. (alum oxide insul. sustained high speeds on pass. Part No. 1557801
All...No. M8 (10 MM) Standard equip. on 1946-48 pass. (alum. oxide insul. sustained low speed on trucks Part No. 559459
All others from 1929 -1950 listed:
1929-31 All...No. 87 (18 MM)
1932 All..No. 86 (18 MM)
1933-40 All No. 43 (14 MM)Heavy duty operation st med. or high speed.
1933-40 All No. 44 (14 MM) Ditto on speed and operatios
1933-40 All No. 45 (14 MM) Average operations
1933-40 All No. 46 (14 MM) Average operations
1949-50 All Pass. 46-5 (14 MM)
1949-50 All COMM and UtIL. 44-5 (14 MM)
This implies that 104s were used for 1941 and 1942 passenger whether low speed or high.
I assume that all the above were AC spark plugs.
Best,
Charlie
