Beware of poorly designed stud mounts! We are finding that a major cause of lost and broken antennas is due to these stud mounts ... and they aren't just the cheap ones either. Beware of the following problems.
ALUMINUM COMPONENTS: Most people realize that aluminum and stud mounts do not mix. Aluminum studs are structurally weak, don't hold threads very well, and quickly oxidize.
INSULATORS: There are many exotic plastics that will work sufficiently as stud mount insulators. But, for common usage, it is hard to beat nylon from the perspective of quality and cost. There are also many poor choices for insulators and many businesses have found them. When your only decision is based upon cost (material, tooling and process), you will normally find the bad stuff. Cheap insulators use "spongy" material that collapses under torque pressure. When that happens, stud mounts vibrate apart, or their threads get damaged from antenna wobble.
BOLTS & WASHERS: Due to constant exposure to the elements, stud mount hardware should be stainless steel. The stud mount is a very critical connection between the coax and the antenna. Rust and corrosion always hamper performance, and enough of it can cause a dead short. Stud mounts should also have a lock washer, preferably the split lock type. Internal and external star lock washers do not work well against plastic insulators. As the teeth sink into the plastic, the locking tension diminishes and you end up with not much more than a flat washer.
THREAD DEPTH: This is a rarely recognized problem. If the stud has spongy insulators and uses a thin star lock washer, or none at all, the "standard" one-inch bolt that connects the stud to the mount reaches too far into the coupling nut. When the antenna or accessory is installed, the threads bottom out before the component is properly seated. This condition causes load stresses to center on the weakest part of the component, namely, the threads. Most antennas and accessories use a thread length of 1/2" (0.500"). The minimum available thread depth in the stud should be no less than 0.540" (overall length plus one thread width). We measured thread depth on some of the most expensive mounts on the market and found the usable depth to be 0.435". These are problem mounts! Firestik's K-4 stud (installed on a standard mirror mount) has 0.600" of available thread depth and the K-4A has 0.680" available. To eliminate problems, thread depth for Firestik products should be a minimum of...0.490" for Firestik, Firestik II, and Scanner Antennas
0.570" for FireFly, and Road Pal Antennas
0.550" for Springs and Quick Disconnects
If you are selling or using non-Firestik stud mounts, you should be cautious. Measure their available thread depth. If they come up short, they are causing problems for your customers, your suppliers and/or you yourself. Needless to say, Firestik views this as a very serious problem. Bad stud mounts cause antenna breakage. Dealers that casually make warranty exchanges, or end users that replace broken antennas without checking thread depth may be treating the symptom instead of solving the problem. If the threads are broken, 98% of the time it will be due to bad stud mounts, antennas that were not tightened, antennas that were over tightened, or those that ran into something that they should not have encountered.