With only 1/8" of thickness a screw has too little to grip. Pop-rivets are designed for shear loading and not pulling as you want to do.
I would use a anchor toggle or similar type of expansion bolt just as you would do when mounting something heavy to sheetrock. A crown bolt hollow wall anchor with a truss head can be found for different thicknesses of material and are designed for situations where there is a hollow space which is what you have with your aluminum studs.
I would hesitate to add a load to aluminum as it does not resist fatigue anywhere nearly as well as steel if there is any flexing at all.
For best results see if you can find a framing stud to mount the Ancra Bolt-on Tie-down over so that all sheet metal screws penetrate the stud. Otherwise use an aluminum heavy duty pop rivet as they will hold a lot more pulling stress than a sheet metal screw without backing will. I've been using pop rivets for years and found them to hold much better than a sheet metal screw without a stud behind it.
* This post was
edited 05/10/12 07:25am by dbates *
Plus New Brunswick, Prince Edward Island & Nova Scotia
Well, just to add a little conflict . . . I'd vote for pop rivets.
I don't know what monel means, either. But I've used lots of pop rivets, in fact, I built a two-seater aircraft once, and used pop rivets extensively. So literally, my life and the life of passengers were hanging off pop rivets. Several pop rivets, I might add. But pop rivets penetrate the hole, then expand 360 degrees behind the hole versus what I consider a fairly small area of contact with screws. Pull them out, and you'll do extensive damage. In fact, drilling them out is the only practical way to remove a pop rivet. So that would be my choice. But I'd probably use some form of stainless steel pop rivets and in any event, almost certainly not aluminum ones.
Added: I don't know for a fact, because they were provided in a kit aircraft, but after six years or so, there were no signs of rust on the exposed rivets. I know they weren't aluminum, I believe stainless steel. I know when I pulled them, the pin broke with sound as loud as a gunshot. I used ear protection.
As a former Assembly Installer/Change Incorporation Mechanic for a major aircraft manufacturer, and holder of an Airframe & Powerplant license, I certainly hope you didn't use Pop Rivets to build your aircraft! First, Pop Rivets would be unsafe in aircraft use, and second, they are NOT FAA approved! I can't imagine any inspector signing off on your build if they were used!
I would think (especially if the rivets were included in the kit) that you were using Cherry Rivets, or Cherry Max rivets (or equivalent). They fasten tighter than Pop Rivets, and the stem is retained by a locking collar for added shear strength. In some areas where high strength is desired, and access to the reverse side is restricted, Blind Huck Bolts might be used.
But, on an aircraft structure, NEVER Pop Rivets!
There is a HUGE difference between aircraft quality blind fasteners and the Pop Rivets that are available at your local hardware store!
To the OP, you can get Cherry Rivets at the parts department of your local FBO at the airport. The last time I checked, several years ago, they were about $1 each. If you have a real strong grip, they can be pulled with a Pop Riveter.
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I use a lot of wellnuts to fasten accessories to aluminum boats. I've never had one pull out or otherwise fail. As a bonus they also form a watertight seal. Here's a link to one supplier showing how they work.
After looking at the Plusnut I change my vote to them. That is how the expandable type of poprivet works but appears to be a better way to go. I have a very similar item in my tool kit but it was called a Blind Nut when I bought mine years ago. Problem with mine is they are aluminum and very soft. Look at the Tri-Grip and Bulb Lite blind rivets.
I like the Wellnuts and Jacknuts as well, think I will get some of those. The Jacknut looks like a Hollow Wall Anchor without the screw. Tool looks like my tool for installing Blind Nut.
There are great things here. I think I'll keep reading the forums.
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