Firestik SS-3M Stainless Steel Medium Duty CB Radio Antenna Spring Mount These springs are made from long lasting, top grade electro-polished stainless steel. Each spring is about 3" The upper and lower inserts are made of chrome-plated machine brass Works especially well with 2ft "KW" & "FS" series antennas as well as the 3ft "FL" or "RP" (lighter weight) antennas. Standard 3/8"-24 threads 100% American made with 100% American materials