This thread might be of value.
I use flanged threaded inserts, pocket milled from the bottom. No way could they pull out. T-nuts would be better if I’m building an overhang on a climbing wall to hang from one hold, but for clamping the m5 threaded inserts I have installed can hold more than enough force. I have 1/4-20 threaded inserts in the layer below my wasteboard to hold it down.
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