I would highly recommend not using Cinder Blocks for jack stands I tried it once when I was replacing the rear axle in my Ram. They held fine until I started using my Impact Wrench on the U-Bolts the high pitch vibration literally shattered the blocks causing the truck to fall on me. Lucky for me the truck was a 4x4 and sat pretty high other then having to change my pants there was no real harm done. I purchased a set of 6 ton stands the next day and have not been with out them since.
Do not use Cinder Blocks if you going to be working with impacts under the truck!!!!!!!!
