Use of Nut Inserts

[lippy]

Originally Posted by Bob Putnam

Tapping a rail that's less than 1/8" thick ain't very strong...

You can install a nutsert without fancy tools.

Drill the hole very accurately.
Insert the rivnut.
Assemble the bolt, nut and washer as shown.
While holding the head of the bolt, tighten the nut to set the insert. A little lube on the bolt threads help.

Here is an update. First, I was able to get the Rivnuts to work with the cap screws Bob recommended. At first, the Rivnut would sometimes turn in its hole. So I took a recommendation I found elsewhere on the web and took a short, stiff section of angle iron about 6" long and drilled a hole near the end just large enough for the screw to fit through. I then inserted the angle iron in between the Rivnut and washer in the diagram above, and held the angle iron from rotating, which prevented the Rivnut from turning. It's important to use the smallest hole possible in the angle iron so the Rivnut does not become distorted by pulling up against a larger hole.

As mentioned in a prior thread, the Pemnuts are sort of slick because they look clean and don't have a shoulder that sits above the sheet metal in which they are installed. The problem is that they are easy to install using a hammer in an unattached piece of sheet metal, but they are difficult to install in tight places. For that reason, I tried to install a Pemnut the same way as the Rivnut, using the tool above (with the angle iron) to squeeze it into the piece of sheet metal. It seems like it worked fine. This may be the ticket.