The Shure mic inserts marked Shure MC125, which is a sealed cylinder with one only 3mm entry hole at the centre of one of the flat faces.. Do you know where I can find data on these?
The MC series of mic elements were discontinued in 1985. The elements were used in the products of other companies for sensing sound. An example might be a sound level meter.
Our records do not indicate a model MC125. Perhaps this was a model made especially for another company and was given a unique model number.