I had the HF 6 ton jackstands that were recalled. Scared the piss out of me the number of times I have been under them. I have always been careful using wheel chocks the vehicle gets lifted.
No more. I returned them for a refund.
This is what I replaced them with
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These go up over 21", very tall. Now I need to get the new Snap-on HF copy Super Duty Low Profile Jack in sunburst Orange



!!
3,000 lbs each. 4x will support 12,000 lbs safely. My old Avalanche was 6,200 lbs +/-. Jack shear pins with with cotter pins prevent any chance of the pins coming out.
Much more secure than trying to guess if you have enough tooth engagement on the ratcheting type stands I used without much thought since I was 16 (many moons ago...on my 69 Firebird in HS). No second thoughts, it is a much better, superior design.
Definitely a factor of safety involved of 1.5x-2.0x, but they don't officially publish because of liability.
Very happy and confident with my set up. More room underneath to work also.
Cut 12"x12" (3/4" thick) plywood pads to cushion the concrete in my driveway.
Cheers,
Nashbalto