Bird's precise 50 Ohm 7/8", 1-5/8", 3-1/8", 4-1/16" and 6-1/8" Coaxial Line Sections are designed for insertion between a transmitter and antenna or load. Each line section is equipped with one or two sockets where Plug-In Element(s), in the desired power and frequency range, are inserted. Double-socket line sections are for simultaneous measurement of forward and reflected power.