How To Install PLUSNUTS In Sheet Metal
Rivnuts (rivet nuts) are the most popular way to add threads to sheet metal, but in mobile applications like the sheet metal on a vehicle (aka van) are thin enough that rivnuts can pull out or get loose and spin. For stronger retention in thin sheet metal, Plusnuts are a lot better. Plusnuts are very popular for Sprinter, Transit and Promaster van to campervan conversions. I've used them all over the Sprinter van to attach things inside and out, and they have worked perfectly.
Installing them is tricky, because regular rivnut installation tools don't have enough length or travel for Plusnuts. Therefore you need a dedicated Plusnut tool. You can make one very easily, which I did to start with, but the problem with these is that it's easy for the Plusnut to spin during install, and using anything with teeth to prevent the Plusnut spinning will damage the head surface, even if it grabs well enough to not spin.
I finally broke down and bought this tool which works great. The downside is that it is specific to a single thread. I use the 1/4in version of this.
The C1000 tool has worked flawlessly. The anti rotation pin did break once, but they had included a replacement, and it was easy to replace using a punch. It's easy to install with a consistent force by using a torque wrench. Its short length makes it easy to install the Plusnut without accidentally bending it out of line.
2 wrenches are needed to use the tool. I have a locking adjustable wrench that works great to grab the base and acts as a handle. Then a ratchet wrench is used to tighten and loosen the nut. Using a torque wrench allows for more consistent install force.
Unfortunately each tool costs as much as the ASTRO 1450 that comes with many different thread size dies.
ASTRO 1450 PLUSNUT AND RIVETNUT INSTALLER
This is the only self contained hand tool for Plusnuts. It requires 2 or more strokes, because each stroke is too small to fully expand the Plusnut (the tool is probably the same as the rivnut tool, but with longer inserts). It's versatile with a range of different threads included, but bulky for working in tight spaces. Hard to beat for the price and includes all the sizes you will need.
WHERE TO BUY
Review of using the ASTRO 1450
I used the ASTRO 1450 to install a lot of 1/4-20 Plus Nuts. It works well, but I feel like it is difficult to install the plusnuts straight (in cramped work areas) and with consistent force. The problem is that the force applied varies depending on where in the stroke the handles are. I often overtightened the plus nuts, and they weren't perfectly straight or centered, and then they were easy to cross thread when installing the screws. I never had the cross threading issue with the dedicated tool shown above. Therefore be careful how much force is applied to the handles during install.
The 1/4-20 installation die also bent a little during the install process, and now wobbles when turning the knob to retract the tool. Yes, the bending was caused by moving the tool during an install, but that is very easy to do due to the leverage of the long arms. I imagine that you need to be very careful with the smaller thread dies.
Pre-bulbed vs Straight
Pre-bulbed Plusnuts are already slightly bulged out and take less force to start expanding, and is the only style you should consider if using DIY installation tool. If using a high strength tool, you can use straight, unbulbed Plusnuts. It will take significantly more force to get these started. The advantage is that a smaller hole can be drilled and retain more strength of the sheet metal.
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