Use jack stands AND wood blocks.. if for some crazy reason one of the jack stands fail the load goes no where as it's also resting on the blocks.. an ounce of prevention is worth a pound of.......ummmmmmm maybe dead.. as for cinder blocks, (construction type) I would not use those. During this past winter, I jacked up my 20ft cuddy and trailer, prob 3000lbs... took most of the weight off the tires and bought (6) 4x8x16 blocks.. they are solid, they worked perfectly for the 6 MONTHS!!! of winter we had in the north east. They did not crack, crumble or chip under that load for 6 months.. I always use stands and blocks when I work on my breaks, axles etc... the stands are actually a "back up" for the blocks... not the other way around..