Unimatch

Unimatch, in the context of stereo headphones, refers to a design patented by Sony which allows the cord to end in either 1/8" or 1/4" jack. This is accomplished by using a 1/8" connector with threading around the base hardwired to the cable, upon which the 1/4" connector can be affixed.

ource

http://bssc.sel.sony.com/BroadcastandBusiness/DisplayModel?m=0&p=10&sp=79&id=52568