I've given up on T-nuts. Such a tedious hassle to get them seated properly and then there's always at least one of a set that manages to blow out right away and two more over time.I only use threaded inserts now. Get them at McMaster-Carr. They thread into the hole with a hex driver and stay put. Even when there's almost no "meat" between the hole and the speaker cut-out. Be sure and get them "with flange" or you'll run them right back out when you tighten down the bolt. Don't ask me how I know that!
They come in any thread size you could want in quantities of 50 or 100 for a few dollars.
![](http://www.mcmaster.com/param/images/insertsplasticwood/knifethrhexflangea.gif)
The only way to fly.