TELEPHONE No. 706 CASES
In the minutes from the British Telephone Technical Development Committee, Subscribers Apparatus Development Sub-Committee meetings it states that Diakon was not satisfactory for cases and and that nylon should be used. As these minutes were about field trails, the history seems to fade......
Be very careful of Diakon as it chips and breaks easily!
The ABS cases were THINNER than the Diakon ones, because they were stronger. This made the moulding cheaper and lighter. This gives another way of telling ABS from Diakon. There were strengthening webs inside to restore the original thickness locally for rigidity, and in some instances to ensure a snug fit. TMC had problems with these, since they tended to cause "sink marks" on the outside, so the webs were made very thin on later supplies, which solved the sinking feeling whilst serving the intended purposes adequately.
Diakon was moulding material 12 and ABS was 17 - these will appear in the moulding marks.
I am not aware that Nylon was ever seriously used. ABS was a very new material in 1962, so the degree of improvement it would bring was probably unknown. The breakage rate of Diakon was still a SERIOUS problem in the mid-60s, as large numbers of Diakon 706s were still in use, and probably being "wiped up" (GPO factory repaired) using local stocks of Diakon mouldings...
Many thanks to Geoff Mawdling and Paul Ebling
Last revised: January 22, 2020