enclosed is a picture of a W.E. 531 subset. what was this originally intended for? No bell, but a relay... could this still be used today?
Like the 306 sets, this was apparently used for 4-party selective party lines, or 8-party semi-selective.
Here are 2 catalog pages from Western's 1950 Telephone & Apparatus Catalog No. 11, 1950, and which Poplar1 has described to a "T", showing the subset pictured, and another variation with a different suffix identifier. The 531CW-3 is described in detail, at the top right of the first page.