Internal Threads

[JamesCH95]

Originally Posted by jee7s

As a general rule of thumb, you need three threads in the material, with at least one exposed thread beyond that. That means that for 1/8" thick material, you need a pitch of at least 24 to properly fasten. That's a lower limit on TPI, and you'd probably want to be higher than that.

Originally Posted by DampRobot

First, I've heard 6 threads, which would make 24 tpi the largest recommendable in quarter inch material.

The number I know is 3 complete turns if the threaded material is as strong as the fastener. Because high-grade aluminum can be about 1/2 as strong as an alloy steel bolt (this is subject to wide variances) 6 turns would suffice.

Now, if the application actually requires the full strength of a selected fastener is a whole different matter...

OP - you might also want to look into rivet nuts, they can be assembled easily and quickly with basic hand tools. I don't want to start a "rivet nut vs pem nut" debate, suffice it to say that they each of their uses, so consider your choice carefully.

Edit: There are also anchor nuts and weld nuts that might work well, depending on your application. Some anchor nuts can be purchased with nylon locking elements and/or floating threads, making them very useful where small adjustments might be needed.