The 4017A had a plug and socket arrangement which was not 100% successful as the plug tended to fall out - not ideal. These photos show the springy connectors in the mic socket together with the plug, the plug lined up with the socket, and the plug inserted - and already starting to fall out!
The next set of pictures show a different form of plug, with screw terminal connectors. Is this a production version or an unofficial modification?
Many 4017A mics were retro fitted with the well known three terminal connections and became the 4017Ac. New 4017s became the 4017C (below). The 4017C remained in widespread use for some twenty years, up to about 1950 - and certainly looked more handsome than the earlier version.