Hello and welcome to The house of Chrome.

 You are looking at two unused AD-1 microphone connector / adapters used primarily on RCA & Electro Voice model microphones but also a few Japanese ribbon mics. RCA used a much wider thread pattern on many of their mics and stands so it was essential to have these adapters to mount an RCA microphone on a standard 5/8 X 27 thread desk or floor stand which the entire industry had embraced at that time except for RCA which continued to make an off size thread patter up until the mid 1960's.

 There's really no point in buying a cheap plastic replica adapter like the ones being sold on Ebay and Reverb for a few dollars less that can easily be stripped or break off in your mic which would cause a big problem. Be safe and smart. Buy an actual metal adapter.

 As seen in pics # 7, 8 & 9 this adapter fits on any desk stand and then allows the BK5A model, 44BX and 77DX model mic to be mounted.

 As you can see in pic the adapter has zero cosmetic wear. Pic # 9 is of the old AD-1 adapter. You can see the slight difference between the original and the newer.

       MICROPHONES SHOWN ARE FOR DISPLAY PURPOSES ONLY AND NOT PART OF THIS SALE.