Designed to be worn under helmets or safety caps. Microphone: M-7A Electret (nominal 50 ohm). Boom: Full flex for precise microphone positioning. Rotates 200°for left or right side placement. Earphone: Lightweight Dynamic (nominal 300 ohm) wired in series. Cord: 4 conductor, 5' Coil. Plug: PJ-051. Microphone on/off button. NRR: 23dB.