[wingnut60]

Ron,
Each block is rated at 6k--doubt that the legs of clev's fiver are carrying anywhere near that much. 5K pin = 2500/jack, nowhere near the design limits. It is the surface they are placed on causing the problem. In your trailer pic, 4 jacks supporting 17k = about 4200/jack--that is about 70% of rated capacity of each block. I would not hesitate to use them on all my jacks if I wanted to pay the cost, but each would be on some type of flat surface between block/ground.
Another of the negatives so far with the blocks is having to center the jack pad in the block--not easy to do before putting a load on them. I have found the magnets too weak to hold the block to the pad when lowering the jack, thus in the auto-level mode, can't get them centered on any but the front jacks before starting the auto process.
But your blocks are certainly first-class....