Key to suffix letters used on BT Special Range Telephones (prefixed SR):

•    A = Telephone with built in Bell or Tone Ringer & without Recall button

•    B = Telephone without built in Bell or Tone Ringer & without Recall button

•    C = Telephone with built in Bell or Tone Ringer & with Recall button

•    D = Telephone without built in Bell or Tone Ringer & with Recall button

•    R = Earth Recall button fitted

•    RR = Register Recall (Timed Break) fitted

•    AR = Alternative Recall (Earth or Timed Break) fitted