Nylocs: Overused & Underused

I ought to write more about fasteners. We use them by the dozen, and even by the hundreds and thousands in a large station. They're ubiquitous. I sometimes buy them individually, though more often by the box. Common ones I can buy at local specialty stores, less common ones I buy online or through contacts in the tower business -- there are suppliers that won't sell retail.

The purpose of a fastener, no matter the type or the material, is to hold things together. They may be metal plates, round tubes, combinations of both, wires, and more. Those used outdoors must survive the rigours of wind, rain, snow, sunlight, corrosion, axial and/or shear loads and so much more. It is no wonder there is so much variety on the market.

Unfortunately for us, fasteners fail. Sometimes it's a mechanical joint and other times it's an electrical connection. The former can pose a safety risk while the latter can render an antenna, and even your entire station, unusable. We want our fasteners to keep things fastened!

Hams usually don't come into the hobby with a deep knowledge and understanding of fasteners. I certainly didn't. We stumble along, using what comes with the products we buy, doing what other hams do or just buy whatever we can find at the local hardware store. 

When a fastener fails we have a tendency to overcompensate during the repair. A common aftermarket choice is the nyloc. They are included in many modern HF antenna products. And why not? They often do a fine job on our towers where vibration and weather shake loose more common fasteners. I use them a lot in my own antenna designs and I have replaced nuts on commercial antennas with nylocs when the need arose. I like them.

They are most useful in specific applications:

• Vibration
• Thermal cycling
• Round surfaces, such as tubes
• Joints that are tightened once and are difficult to access afterward

Some hams, encouraged by initial success, start to use them everywhere. That can be a mistake. In many applications they can cause more problems than they solve. It is not a universal solution to our fastener woes. There is a large variety of fasteners for that very reason. Each has its range of application. 

Here are a few items to consider before choosing to use a nyloc:

• Material: Are the nyloc, bolt and work surface compatible? A poor choice can lead to galvanic corrosion, galling, erosion and difficulty removing the nyloc at a later date. I almost always see stainless nylocs used since they are most commonly stocked. Even stainless on stainless can be a problem since different stainless alloys don't always play well together.
• Grade: The nuts and bolts should be the same grade, for example grade 5 steel and 304 stainless. Otherwise threads can be stripped, they can gall and occasionally fail during tightening or later when under load. Nylocs must be carefully selected as for any hardware.
• Ease of use: I have seen nylocs used in place of the manufacturer's recommended fasteners for splicing tower sections. That may seem like a good idea but really isn't. First, you will rarely see stainless fasteners spec'd in this application, and there is good reason for that. Shear loads have their own requirements. The choice of nuts also matters. Have you ever tried to assemble or disassemble a tower that uses nylocs? It is very fatiguing when hanging off the side of a tower. The reason is that high torque must be applied on these large fasteners for many rotations of the nyloc rather than just for a moment for an ordinary nut and lock washer. 
• Reuse: Nylocs can be reused within reason, and I do. But for how many times? There is no reliable answer. Do you really want to bet on it holding after using it for the third or fourth time? I've discarded nylocs while attempting reuse because when I judge that they didn't grip properly. When in doubt throw it out.
• 
  Plastic surfaces: Nylocs to secure electrical connections on plastic enclosures are often problematic. One example I've run into several times is the Cushcraft XM240 balun. The studs that connect to the driven element grip the enclosure with a conventional nut and lock washer, while the wire lug is secured to the stud with a nyloc. The large torque over many rotations of the nyloc caused the inner lock washer to abrade the plastic so that the studs loosen. In my experience it is a common cause of intermittent connections. The feed point is out of reach so the antenna may have to come down for repair. I've seen the same on other products and on my home brew projects.

If not a nyloc, what are acceptable alternatives? As always, it depends on the application. There are so many alternatives that it can be dizzying. 

Luckily only a few suffice for the range of applications that a ham is likely to encounter. Here are some that I use, or that I've encountered but don't use.

• Lock washer: This is hardly surprising since it's the single most popular device for securing a nut on a bolt. The problem is that there are so many types. Spring and star (internal or external) are the most common, and it is unusual to bother with others. 
• Keps nut: These clever devices have an exterior star lock washer incorporated into the nut. They are specified on a variety of Trylon towers that are in wide use in Canada and in the US. They occasionally show up in other products. Large specialty stores will have them, but otherwise you'll have to order them online.
• 
  Jam nut: Instead of a lock washer, a flat washer and two nuts are used. The outer nut is the jam nut. It can be an ordinary nut but there are special nuts made specifically for this application. First you tighten the inner nut as usual then, holding it fast, tighten the jam nut against it. Contacts tell me that jam nuts are becoming increasingly common in commercial tower projects in lieu of lock washers.
• Chemicals: Probably the one most have heard of is Loctite. There are many varieties on the market from them and other suppliers. I never use chemical locking compounds on towers and antennas. Indeed, I am more likely to use a long-lasting grease on threads to retard rusting, prevent galling (stainless) and ease removal years later. A properly employed fastener will hold fast when lubricated.
• Compression clamps: These include hose (or gear) clamps, while others use a conventional bolt and nut to tighten the clamp. They are mostly found on telescoping antenna elements and light duty mast. They are easily damaged by excess torque so use them with due care.
• Wired nuts: They are often specified in high vibration environments such as aircraft. Prop pitch motors use them. Most hams discard them when servicing old equipment since they are difficult to reuse or replace once disassembled. The matching bolts have holes through which the wires pass.
• Thread deformation: For nuts that will never be removed, the bolt threads emerging from the nut after final tightening are deformed with a hardened tool. The nut can't come off, ever. I've seen this technique occasionally used on commercial tower splice bolts. Those towers are meant to be cut down at the end of service life, not disassembled for reuse.

That was a very long-winded way to explain why nylocs are not a universal solution for securing fasteners. I recommend avoiding them where they are inappropriate, but do use them when they are the best solution. Don't select fasteners out of habit, myth and lore, or because they happen to be available. When in doubt, use only what the manufacturer recommends.