Made to Spec MIL-J-641, contact springs are of special alloys for long life; insulation is high-dielectric strength phenolic, tinned terminal lugs for easy soldering; short frame; mounts by 3/8-32 threaded bushing and nut; open circuit. Available in microphone jack which is 3-circuit, 1/2 oz. weight, or headphone jack which is 2-circuit 1/3 oz. weight. Stereo is double open circuit, three conductor jack.