When the situation occurs and you need to interconnect a phone instrument with an audio system to either provide a source for a particular show in progress or to feed a tape recording or other show material back to a central point, be prepared with these unique adapters. . . the Model HK-117T or HK-117R; "T" meaning it uses the transmit portion of the telephone instrument and "R" meaning it uses the receive portion of the telephone. These adapters make the job 100% easier.