I remember dgage posted about them at that other place. Just for you, I went against my self-ban from that place (LOL) and found one of the threads in which I remember him having posted a link for the "slab nuts" he uses in his line of HT subs. Here it is:
https://shop.stafast.com/weld-nuts/s...s/sl14205h2170
Here's the thread:
https://www.diymobileaudio.com/threa...nd-mdf.392314/