I have a mic labeled Shure Model 555 Unidyne Dynamic Microphone." It looks very old, but does not use a standard mic cable. do you have adapters for it? It still has three holes, but also has a threaded section.
The 555 used a 3 pin Amphenol connector, part #MC3M.
You can get pre-wired cables from Tom Ellis (214-328-3225)