RivNuts – what are they and how can they help? By Nigel Tolley
Perhaps one of the most frustrating things about tapped holes is when the thread is ruined. Another issue is when there is only a thin sheet or thin-walled tube, and you would really like to attach something removable to it.
There are two or three options: you can drill out the hole and retap it (if there is enough material and enough room) or you can use a helicoil repair kit (if the material is thick) but in thin material you are out of luck. And, if a thread has pulled through thin or soft material before, it is likely to pull through again. Tapping freehand is also a pain - a snapped tap can easily be uneconomic to remove from a part, leading to it being scrapped, with all that results. Plus you need to buy a new tap!
Instead, we can use a rivnut. These handy devices are a sort of cross between a rivet and a nut; the real beauty is that you only need access to one side.
A rivet nut, also known as a blind nut or nut-sert, is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side. There are two types: one is designed to form a bulge on the back side of the panel as a screw is tightened in its threads. The other is similarly drawn in using a screw, but is drawn into the sleeve instead of creating a bulge.
That's the entire extent of the article, so I'd better translate it into English and expand a bit on the uses.
Ideal for blind holes, they thread onto a setting tool which operates a little like a pop riveter, which sets them in position as they collapse inwards in the same way as a pop rivet would. Once the rivnut is set, the tool is unthreaded from the fixing, and the larger hole is now effectively filled by a ready threaded smaller hole. The next step is simply to thread in the fixing bolt. Job done.
The photos show a red and black rivnut setter. This is serious overkill for the locksmith, costing £450, running off compressed air and being designed for production settings. You present the rivnut and the ferrule automatically spins to set the rivnut onto it, ready to go in the hole. Once in, a press of the trigger pulls the ferrule back, setting it solidly into position. Once set, the only way to remove it is with a drill, and the setting tool automatically reverses the ferrule which pushes the tool safely clear of the work, where you can very rapidly set it up for the next use.
My father's company uses this tool to set 4 of these M6 steel rivnuts into 9mm holes in stainless steel tubing, to which the legs of the stainless steel running bars are fitted to hold them securely onto the vehicle. Although in theory the fixing could deform and be pulled through the hole, once a bolt is in the hole, there is simply nowhere for the material of the rivnut to go. This leads to a very, very strong fixing.
For locksmith use this isn't practical, but there is a mechanical version which is rather cheaper and, as it happens, more flexible in use. You can pick up what looks like a regular pop rivet tool that in fact sets rivnuts up to M8 for about £30, but I bought a kit for just under £100 from Machine Mart which works very well, and as well as setting rivet nuts up to M12 it also converts to a pop riveter and, even more usefully, into a bolt riveter! It is a great and still fairly inexpensive "Get out of trouble" device. You can see the setting tool in the pictures - it looks a bit like an odd bolt cropper.
Of course, as well as knowing how handy a pop riveter can be - I replaced some cabinet locks yesterday which were held in by 6 of them, and the job would otherwise have been impossible to do - you are probably now thinking "Bolt riveter? That also sounds handy!" And you would be right. These are rather harder to find, but are basically set into holes and leave a threaded stud behind, to which you can then attach things with a regular nut. Good luck finding these for sale, though: eBay is the only place I've found any.
You can see from the picture showing the nuts side-by-side how they expand. They set into the hole in a very similar way to a blind (pop) rivet. I would be wary about using one of these in place of a pop rivet but if there is no other way and the hole is afterwards filled with a bolt, then it will be very tough to shear.
For those of you working routinely on aluminium and steel doors, you are likely to find a few uses for these genuinely handy additions to your toolkit, and when you do they are likely to save you quite a lot of mucking about.