[BCA]

If you look in any CMP parts book printed after 1943 or so there is a column to the right of the part description for a "Proprietory or M.T. Number". Not many entries are made in this column but a typical entry might be NA/GB150224.
I have an undated cross reference book titled "Neutral Numbers" that lists a series of sequential numbers from AG2 to BR192149 with their equivalent manufacturerer number (Ford, GM, Chysler etc).
The numerical parts of the numbers are sequential but periodically the prefixes change: starting with AG, then AT, AL, AE, AN, AB, AM, AC, UJ, CL, GB, FA, RA and finally BR.
As an example: from parts book C60L-03: "Ball, steering shaft" is part number 104918 but the Proprietory/M.T.Number is NA/AN 40004. My Neutral Number cross reference book lists this as equivalent to GM 104918, GM 147485, F 353076S and C 104918. (F-Ford, C=Chev(?)). The NA prefix presumably refers to North America.
It appears that the Neutral Number system was devised to standardize all of the manufacturer part numbers (much like the US did with the "G'" number system for vehicle parts) but was never fully implemented for CMP's. Maybe it was commonly used in British parts books.
Can anyone clarify when this system was developed and if it was ever widely adopted. I assume that by the mid-1950's everyone went to the Federal or National Stock Number System that is used to the present (e.g.: 5330-00-741-0741).
........ Brian