1 pin 3.5 mm for Retevis RT22P; walkie talkie earpiece is only compatible with Retevis RT22P RB19 RB19P B3H B3S two way radios ^^ Clear sound quality; walkie talkie earpiece with mic and speaker; speaker impedance is 32 ohms and mic sensitivity is 38 for crystal clear audio ^^ Provide private calls; two way radio earpiece adopts air conduction transmission design; in-ear earplug make calls more private ^^ Side PTT; 2 way radio earpiece features compact side PTT which is easy to operate and press ^^ Detachable; interface between walkie-talkie earpiece covert tube and wire can be disassembled; it is convenient to clean covert tube