I've had these on my Delta contrator's table saw for a while now and they're great, handling the cracks in the floor with ease.  They're easy to operate, locking securely and rolling smoothly.  I've since bought several more to put on other tools in my workshop.  What a great value they are.  As others have stated, the M-12 size metric nuts and washers are easily found, so installs have been a breeze for me.