Friday, June 13, 2014

Renewing Old Hardware

In many cases it is more economical (time and money) to buy new hardware to replace rusted and damaged hardware rather than to repair the old hardware. Since most of us purchase used towers, antennas and related paraphernalia that must endure the elements we often face this question.

When it comes to hardware that is non-standard it can be quite expensive to replace since the only source is the original manufacturer. Such is the case with many towers, which I why I cautioned about this point in my recent article on buying used towers.

If you prefer to renew old hardware rather than spend money on new, expensive replacements, read on. In many cases it is possible to do so with a modest investment of time. What follows is how, earlier this week, I renewed the tower bolts on my used DMX-52 tower.

You'll need a few tools:
  • Tap and die set. No do-it-yourself'er should be without one of these. You say you have no need of one? You're wrong. Although their primary intended purpose is cutting threads in metal stock -- taps for interior threads and dies for exterior threads -- they work wonders on old, damaged threads.
  • Wrenches. To hold the nuts and bolts being cleaned.
  • Machine oil. Used to reduce friction and heating on the cutting surfaces of the taps and dies, and to recoat them afterwards to inhibit rust. Even when just used to clean rust the hardware and tools can get surprisingly warm. The temperature of the working surfaces is much higher, which can damage the tool and hardware if cutting is done dry.
  • Grease. To protect the hardware after renewal.

I bought my tap and die set many years ago (upper right in the picture). It has a wide range of matching taps and dies up to ½" SAE and equivalent SI. It's important to correctly identify the thread pitch before applying the tool to the hardware. In the case of the DMX bolts there are two thread diameters: ½" and ⅜". The thread pitch is NC (National Coarse) so if you use the NF (National Fine) tools the hardware will be ruined.

Apply a bit of oil to the cutting surfaces of the tap or die and carefully thread into the nut (or onto the bolt). If binding occurs you probably haven't properly aligned the tool and hardware. Back off and try again. Once you have positive traction with the tool use a wrench on the hardware and use moderate force to cut through resistance offered by rust or bent threads. On the bolt be sure to advance the die right up to the head.

If you've done it right you'll find that the nut or bolt can be unthreaded from the tool with just your fingers. The cleaned nut and bolt will thread together without appreciable resistance. The elapse time to clean each nut or bolt can be as little as 1 minute, but don't rush matters if you are inexperienced with these tools.

In the picture you can see the rust and debris cut from the just-renewed hardware. The pile grew larger by the time the full bag of hardware was processed. Loose debris left on the tools and hardware after cutting should be brushed off.

Once cleaned and checked the bolt threads (and, optionally, all surfaces) should be coated with a durable, outdoor-rated grease. I use white lithium grease. It's inexpensive, easy to apply and clean up, has a wide temperature range and is good at repelling water. My 500 gram tub of grease is practically a lifetime supply. I also use it in rotators, where it has proved durable and compatible with -25° C temperatures.

Grease on the threads will not result in the hardware loosening over time if the hardware is properly installed on the tower. That requires applying sufficient torque to enable the lock washer to do its job of preventing hardware rotation during the lifetime of the tower.


It is not my intention to provide a tutorial on the care and use of taps and dies in this article. You should learn how to use these peculiar tools from someone knowledgable or (if you're careful) books or internet resources. The cutting surfaces are fragile, very sharp and can be damaged (or injure you or damage hardware) if not correctly applied.

The tower bolts I am renewing are Grade 5 strength. Although the taps and dies are harder yet you should be aware of the potential for damage if the tools are of unknown quality or the hardware is of unknown strength.

There is less risk in this specific case since we are cutting rust and debris, not the high-strength base steel. Oxidized steel (rust) is relatively soft. It also has greater volume than virgin steel, which is why rust seizes threaded hardware. But this is also why it can be removed by the method I've described.

1 comment:

  1. This is awesome! Why replace when you can renew an old one? However, I have to agree that one should be quite familiar with the usage of those tools, and not jump into the process with scant knowledge about the method. Nevertheless, thanks for sharing this with us!

    Hubert Bates @ Tab Data Systems


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