If you took the proven features and performance of the famous KW" series antennas and added a unique tuning mechanism to the top. you would own the equivalent of a Firestik II. "FS" Series antenna. Aside from the ease of tuning. the patented design broadens the antennas bandwidth to keep SWR lower over more channels. The upper coil extension also increases the power handling capability of the antenna. All "FS" antennas are compatible with autos. trucks. vans. motorcycles and ATVs in a single antenna configuration when metallic ground plane is available. Or. they may be used in dual (co-phased) configuration on any vehicle made from any type of material. Like all CB antennas. the "FS" antennas should be fine-tuned (SWR) in their final mounting location. If you have ever tuned a non-tunable tip antenna. you will have a real appreciation for the "FS" antennas. To tune a "FS" antenna. you just pop-of the tip and turn the adjustment screw up or down as needed. All "FS" antennas exceed the requirements of any CB radio. new or old. Aside from the hi-performance loading coil that maximizes the transmit/receive functions of your CB. these top-loaded antennas will also receive the NOAA emergency weather alert and national weather broadcasts for radios with those features. The "FS" antennas are 100% American made with 100% American materials. To maintain a balance between flexibility and ruggedness. we use a custom blended. glass fiber reinforced shaft. Each is wound with heavy insulated copper wire to prevent the oxidation and shorted windings often found on non-Firestik antennas. The tunable tip mechanism is made from rust-proof brass and has a rubber O-ring to hold the adjuster in place after tuning. Our 3/8"-24 threaded base has a tapered contact point that works especially well with Firestik mounts and accessories. The tapered "lug-nut" effect transfers stress away from the threads and reduces the possibility of vibration induced loosening of the antenna in its mount. Ea"4′ Firestik(R) II FS Series Tunable Tip CB Antenna – 900 Watts Black FS-4BK