I guess you can't really see the inside of the leg mount from my other pics. Here is an example of the flanged nut style used, about 5/8" of threads. I also spot welded the back side and drilled the opposite side of the tube to accept the extra leg length.
If I was starting the steel stand from scratch I would have done a few things different but I think this will do the job, held this tank up for nearly 15 years already
Thanks for the kind comments, it's shaping up nicely and I am really glad I changed from a corner overflow to the 48" Calfo with a Bean Animal drain, very quiet and pulls a huge sheet of water off the top. The closed loop will be interesting to tune once the sand and rock are in as well. Hoping to hide all of it.