Years ago I tested quite a few brands of thread. I found Maxi lock to meet all my needs from my sergers to industrial machines.
I have sewn for a number of different clients in my workshop. All of them included Maxi lock with their job. This is how I found out that Maxi lock does make a heavier weight on cones that contain 6000 yds.
Strength test your thread by taking it between both hands and trying to break it. Pretty hard to do.
I have used it on bridal wear to heavy duck civil war costumes to replacing zippers in work jackets.
Many slipcovers and draperies have also been done with Maxi lock from my workroom.