Phase inversion switch.
The connection of mine is DIN (kind of small 5-pin XLR).
I use it as microphone singing has been saying and sometimes on snare drums.
It is a fairly balanced micro combined heat and shine. At this point it competes with Beta57 and more gentle.
It is much less dull than a SM57 (and SM58) with an optimal view.
It has an output level of less than one but greater than a Beta57 SM57.
It is a micro found regularly on ebay around € 40. What makes a microphone excellent value for money. In addition it is solid and does not seem to deteriorate with time.