GPO, POST OFFICE and BT
MANUFACTURERS CODES, COLOUR CODES
& MOULDING MARKINGS

The British Post Office (BPO) purchased telephones and other apparatus from various manufacturers.  On a lot of equipment the manufacturer can be identified by the use of a manufacturers code.  Where a PO factory code is shown, that means that the equipment has been made or refurbished by one of the BPO factories.  Quite often these codes are on labels stuck over the top of the original manufacturer's code.

It is clear that the original single-letter and later double-letter codes were allocated with fairly little regard to any logical meaning.  Once all codes were expanded to at least three letters greater care was taken to make meaningful combinations.  Existing two-letter codes were expanded by suffixing 'A' to the original code.  The list also includes some non-BPO codes commonly found on telephones (AP, YA and Z).

Thanks to many articles from the Telecom Heritage Group, especially the lists compiled by Graham Wooten, Andy Emerson, BT Museum and John Ferris.

Code Letters

British Codes
Note that type numbers of telephones beginning AP or Z are not BPO codes. AP stands for Admiralty Pattern, denoting a Royal Navy design, and YA and ZA are British Army prefixes. A pattern number starting 10A (or 10 followed by another letter) is Ministry of Defence. Type numbers beginning H are generally ATE products (the company originated at the place of Helsby), N denotes British Ericsson products, S are Siemens Brothers or AEI numbers, TEL is normally GEC, whilst a number beginning SA on BPO instruments denotes Subscribers'  Apparatus, generally a pre-release prototype or an item made specially for a particular customer.

Australian PMG manufacturer codes
Manufacturer codes were allocated by the Postmaster General are generally as for the BPO, with the addition of B.I. and B.I.H., which both indicate British Insulated Cables Ltd, located at Helsby. The ATM company was a spin-off of B.I. which itself merged with Callander's Cables Ltd and became BICC.

New Zealand
Some telephones made for the New Zealand Post Office carried the initials HCUNZ, standing for H.C. Urlwin of Christchurch, New Zealand.

Moulding Products
Code Letters allocated to Manufacturers

Moulded items are marked with the manufactures code.  Where manufacturers supply moulded products, which are parts of instruments, to other firms, then the combined code letters form the manufacturers of the moulds, together with the contractor for the instruments will be shown as follows:- 

e.g.             S               Siemens brothers (for manufacturer)
                MPL           Moulded Products Ltd (for moulded product)

In the above example the upper letters indicate the item manufacturer, the lower letters the moulding subcontractor, followed normally by a number or letter which represented the type of moulding material.

Examples of the codes are shown below:-

Made for W by C and the moulding material is 'BA'	Made by PX for PX and the moulding material code is '1'
Made by Ericsson for Ericsson and the moulding material is '1'	Made by Ericsson for TMC and the moulding material is '4' Not sure about the M and CL

Made by LR for FH and the moulding material is'M'

 

THREADS FOR CORDAGE, WIRE, CABLES, ETC.
Colours allotted to Manufacturers

Within cords and cables there are coloured cotton threads which identify the manufacturer.  These colours are to the British Standard for the Commonwealth and coloured threads are always listed in alphabetical order (British Standards PD 2379 - 1956).

Title Codes

All BPO equipment, large and small, carried a 'title number'.

As well as the title number, telephones normally carried a mark number and the date of manufacture. Normally the original design is known as a Mark 1, the first modification as Mark 2 and the second as Mark 3 (and so on).  But the GPO modifications, up to around 1940, were identified by three digits, starting with 234, for the original design (Mark 1), then 235 for the first modification (Mark 2), 236 for the second modification and so on.  Nobody can explain why 234 was the first iteration and when the changeover from the early "23X" markings to the later "Mark X" style occurred.

Examples:-
The labelling 'Telephone 162 C34/1' indicates title number 162, made by GEC in 1934 to the Mark 1 design.

Under the older scheme of labelling this would have been shown thus:-

 C34    No. 162
 234

Moulding Colour Codes

Mouldings also had a colour code, but this was only used in specifications.

Click here for the colour code list.

Last revised: December 24, 2024