Flight Helmet Straight Drop Communications Cord for Boom Microphone and Earphones. This cord is used when using a CX-4708 Helmet cord and switching configurations between a boom microphone and an oxygen mask fitted with CX-4707 cord. This cord connects directly to the boom microphone (no separate boom microphone wire needed) and helmet CX-4708 helmet cord. It has a U-174/U plug to plug into aircraft. This cord still allows the use of CX-4708 Helmet cord which is used with CX-4707 oxygen mask cord. New Condition. Made in the USA.