Communication converters adapt (8 OHM) military helmet or headset to civillian (150 OHM) (VHF) radios.  These converters amplify the microphone and increase the impedance on the earphones.

Choosing your cord:

Description starts with the jack(s) on the helmet side and ends with the plug(s) on the radio side.

TP-120 is single plug or Jack(U-92)

P5568  is two plug General aviation plugs or jacks

Available in 12", 36", 48", and 60"; or call for custom lengths. 

Other items you may need:
M87 Microphone Element
19 OHM Earphones