If you don’t know about these, be prepared to learn a “secret”…

This is a small deviation from the usual format since the tools and consumables I‘m going to discuss in this Mailbag are from Amazon, and not electronic “mystery meat”. These are well known and so many of you will already be using them. I recently bought a couple of new tools and the supplies for them, and I realized that some of you are blissfully unaware of something you might find very useful indeed.

Some things are just so perfect for doing “clean” and “professional” projects. For example ”Pop Rivets” (or blind rivets) that use a tool to compress the sometimes inaccessible back side of a rivet and, when properly applied, make a solid, low profile connection of parts immune to vibration and casual tampering. They can lend a professional, finished look to your project as well.

I remember when Pop Rivets brand blind rivets began to be marketed to the general public. Every handyman (real or self proclaimed) had to get a tool and rivets and pop rivet everything. Sometimes, threaded fasteners are better—nonetheless, having a rivet tool and a selection of rivets in your fabrication armory is now de rigueur and it is satisfying to grab them for deployment when they are The Right Thing™ for the job.

But obviously this edition of Mailbag isn’t about Pop Rivets because who doesn’t know about them? No, this Mailbag is about a cousin… or sister… or some sort of close relative of Pop Rivets: Rivnuts. These amazing things were invented only a little after the blind “Pop” rivets and sold by B.F. Goodrich in the 1930s under the brand name “RIVNUTS”. The patent, filed in 1936, and intended to attach deicers to aircraft wings.

The generic name is rivet nut but everyone calls them ”rivnuts“—while RIVNUTS® is actually a trademark of Böllhoff, Incorporated USA—a member of the Böllhoff Group which is based in Germany. Böllhoff focuses on joining technologies and sell other things, including HELICOIL® thread repair inserts for which they have worldwide rights.

But despite the very high quality of Böllhoff products, outside of the high tolerance and performance requirement space of industrial manufacturing, most rivet nuts are rivnuts (all lower case and no “®”), and no surprise, manufactured in China. And, for mere humans like us, these are quite good indeed.

The bottom line is that rivnuts let you put a very solid, threaded hole into a thin panel. The entire thing, done right, is very strong and will not twist under tightening until you exceed the strength of the rivnut or panel material. They are installed from one side, and no access to the back of the panel is required. The result is a very strong, durable, and precise assembly that looks very professional.

Like Pop Rivets, rivnuts use a tool with a mandrel and pulls and compresses the back portion of the rivnut against the panel, effectively crimping it in place with an expanded ring on the inside which pushes the panel against the rivnuts external flange. The generic rivnuts usually feature striations that run parallel to the shaft which assist in the uniform formation of the ”bead” that holds it in. There are variations, though, like hex body nuts designed to go in hexagonal holes for even more twist out protection, and rivets with axially oriented cuts designed to form four “legs” that provide additional pull-out resistance for thinner materials. (the attached catalog from Böllhoff is very informative with many styles and some good background)

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an example of an installed rivnut being used to hold a panel to a square tube
As an aside, rivnuts can also be used to attach panels together. The resulting threaded hole can be ignored, used for mounting, or filled with a screw. The rivnut assembly with be very strong and durable.

So how can you get into rivnuts without cashing out your investments? Chinese companies don’t just produce the rinvuts they also make decent if not industrial grade tools durable enough to be worth owning. This entry was prompted when I recently refreshed my rivet nut capability with the purchase of two tools and a rivet nut assortment from Amazon for a very affordable outlay.

Rivet nut installation tools are simple things. The have a pair of handles that can pull the hardened bolt which is the operating mandrel back torwards an anvil. The rivet nut is made to so that the threaded section is towards the rear and there is an unthreaded section directly behind the flange which is up against the face of the panel it is being installed in. As it pulls, the unthreaded section, being unsupported by the mandrel-bolt collapses in a controlled manner to form the clamping bead that hold the rivet nut in place and clamps the parts together it is passed through more than one thing before installing.

The image below gives a good idea of the internals of a rivet nut. The length of the unthreaded portion must be matched to the intended panel thickness for a proper installation. Each size will have a range of thicknesses it can accomodate.

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a cross section view of a Böllhoff HRT (High Resistance Thread) RIVNUT®, the everyday rivnut will not be Class 12.9 capable!

The mandrels are interchangeable allowing one tool to install a range of sizes. Tools also come in a range of handle lengths and configurations (e.g.: compact, right angle, high leverage). The larger nuts, unsurprisingly, need more compression to install and rivnuts can get very large—the larger tool I bought includes M12 and SAE ½-16 mandrels, I haven’t tried to use these sizes and will probably have little reason, but I am not looking forward to the effort I expect it will require*.

*there are hydraulic, pneumatic, and drill powered rivet nut installers for large or frequent use. The latter can be gotten pretty cheap but I have no idea what the quality and longevity of the cheap tool is

So, what did I get? I bought two tools—one compact, low profile tool with a 90° head for close quarters and fewer/smaller rivet nuts; and one larger (16” handle) inline head model for the larger sizes and numbers. Both are by a Chinese company whose name is the typical unpronounceable type: AIUITIO. This seems to be AUTO with interleaved Is, but who knows?

The low profile tool is a kit with the 8” right angle installer, 9 mandrels of mixed SAE and metric sizing, a scanner for mandrel changes and maintenance, and 10 rivet nuts for each mandrel size. It comes in a fitted, double-sided case with the tool and all but one mandrel on one side and the supplied rivet nuts and one overflow mandrel on the other in the usual tackle box like compartments.

There are not enough slots for all the sizes so I put them in heavy duty ziplocks, labeled them, and fit the rolled up bags, labels visible, into two of the vertical slots. This worked out well, and gives me a sort of rivnut jump kit easily carried around. This all runs about 40 bucks at the time of writing but I got it on a discount for ten bucks less, so you can keep an eye on the pricing and maybe get a discount.

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this kit is enough to get you started, but you will certainly want a better supply of rivet nuts on hand

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I primarily use metric sizes for anything I am building but the SAE sizes come in hand for repairs and existing fasteners

The 16” tool is also a kit, this one in a blow molded case which seems destined to hold up fairly well and has spots for all but one of the mandrels which is stored in a random compartment. The included rivet nuts are basically just shoved into the case where they will fit, and I moved them to a Plano box, sorted and labeled. Like the smaller tool it comes with a selection of mandrels (13), but not as small on the lower end and much larger on the upper. This kit, at time of writing, is 56 bucks, but I bought this for about 10 bucks less as well—sales are your friend.

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more mandrels, more rivet nuts, and more leverage

The tool also has a very nice feature not present on the smaller one: it unscrews itself from the rivet nut when you open the handles after installation. Obvious with a few seconds of contemplation is the requirement to unscrew the mandrel from the rivet nut when you are done. Normally, this is done with knob inline with the mandrel. It’s not hard but if you are doing a lot of rivnutting, especially with fine pitch fasteners, it can be tedious.

This tool has a helical screw in the center that winds back the mandrel-screw with opening the handles. This takes away a lot of the tedium, though it takes a few tries to be comfortable with it. I think it is a very good feature to have. Of course the longer handles means more leverage compared to the 8” handles of the smaller tool. This is important because while the smaller sized rivet nuts are pretty easy to install with the 8-incher, as you get up to 5mm and above, the hand strength required is not trivial. Installing one or two larger nuts is fine but any more than that will be an occasion for regret.

I got two more items to make gearing up for rivnuts complete: an additional assortment of rivet nuts, and a step drill covering the common sizes I am likely to use. The former is part of my habit in cases like this. Having a good supply of consumables keeps projects on track and can make repairs much easier by having The Right Thing™ on hand and not always whipping out the CA or hit glue and hoping.

The latter is something that is frequently included in the kits but was omitted from the one I chose. Step drills are a bit of a morass. Cheap ones are pure junk and good ones can require floating a home equity loan to buy. Finding a good compromise can be hard. But I think the one I chose worked out well. It’s not a Milwaukee, but it’s not Harbor Freight either. It is a double straight fluted bit with 4mm capacity and diameters from 3 to 13mm in 1mm steps. The general rule is that (for metric sizes) the hole size is 2mm larger than the screw size (e.g. 3mm uses 5mm, 7mm uses 9mm, &c).

So, if you know about rivnuts, you know the satisfaction of using them to add that high integrity professional touch to a project, and if this is the first tie you are hearing about them, or you’ve heard/seen but never looked into them—you are in on the secret.
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Ya’akov
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