These military, combination receiver/transmitter headset combos all have a switched cord terminating in either a U-77 or a U-161 plug and are for use with Telephone equipment SB-22 and TA-312. J. Marshall Reber 165 Berkeley St. Methuen MA 01844 Tel/Fax: 978-683-6540 Alternate Email: reber at alum.mit.edu