ALPIDEX 250 Zinc-plated T-nuts M10 13 x 25 mm for Climbing Holds four pronged T-Nut pack of 250

You need to really wallop these to get them in to the plywood and I mean wallop. used a wooden mallet and got blisters from the process. In a wall of about 40 holes I managed to get two loose ones which popped out the back when I screwed in the nuts and then started eating away at the wood from behind when I tried to remove them - requiring me to remove the whole panel to fix them - which was a pain. You can get ones which have little holes for screws to stop them rotating and if I could have a do-over I'd use them instead. That said, the ones that stayed in seem sturdy and do the job just fine. Just be sure an fit them tight and check and double-check the fit. They'll do.

PLEASE AVOID. Wasted hours of my time with these. I've built a number of climbing walls and used t-nuts from other suppliers with zero issues, never broken a single one. These t-nuts however suck, broke more than 10 of them on installation. The legs break really easily because of the way they're manufactured. CRAP QUALITY.