These are thin metal diaphragms used for the 557B  receiver element  on an E1 Western Electric handset. The E1 handset is used on the 202 and 102 telephone as well as many others. This were manufactured for the Old Phone Shop

They measure 1-3/4 (1.750) Diameter by. 006 inch thick.

Original are better but these work nicely too.

We sell original diaphragms also.