Tapping for Mast and Boom Screws

[Marksman]

I have used rivnuts in the past in the commercial aircraft industry, but only when nothing else will work. Friction, (unless you wet install with adhesive which causes it's own problems as it acts like a lube untill it cures) is the only thing preventing the installed rivnut from spinning in the hole. Once installed you must take care not to over torque the fastener used in the rivnut or it will turn in the installation hole and you may never get the fastener back out again without cutting out the rivnut. You can't drill the fastener as the rivnut will simply spin when the drill but tries to bite. Sometimes a rivnut will botttom out when collapsing before it has clamped to the substrate in which case you have trouble even getting the gun off of it because it just spins in the hole rather than allow the gun to dethread. In my 23 years with aerospace I have never seen them used for anything more demanding than decoriative trim installs, never structural, and then only when assembly/asthetics requirements will not allow for anything else. I can't advise against them more!

[clockwork orange]

I have used rivnuts but only where we needed to instal something that needed to be removable to thin sheetmetal where you couldnt access the back to use a nut and washer or backing plate.
Steve.

[delmarrey]

A lot of good info here! As a Machinist that has worked in the electronic cabinet industry (thin metals) and knowing rigging and for a shear application I'd go with drilling and tapping with a fine threaded tap. And go with the shortest screws possible, not allowing more then a couple threads sticking thru to the other side.

Also drill one size smaller then the chart recommends. The charts are for 75-80% thread. A smaller hole will give you 100% thread. In aluminum every little bit helps. Be sure to use a wax or thick grease when drilling and taping. Alum. tends to gall when it get hot.

Over time if the threads wear out then you could go with Rivnuts or rivets. IMO Rivnuts would be for something you plan to take off and on a few times, expensive too. But still use the TefGel whatever you decide!