Wow! Absolutely fantastic! I had several huge boulders in the way of a foundation I'm digging for an extension to the house. I considered buying a rock hammer excavator for $1500 a day to dismantle and transport them. First, I decided to try this ancient method of splitting rocks. 10 assemblies come in a very nondescript tiny box with no instructions. But I watched a few videos online and I knew what to do. I drilled holes with a 9/16 masonry bit every 5-6 inches along the line where I wanted to split the stone. Blow off dust with compressed air. On the advice of another reviewer, I lubricated the wedge and washer assemblies before inserting them into the holes and aligned the washers to direct the wedge's force perpendicular to the desired parting line. Then I tapped them lightly with the mini sled, one tapped each, then the next, then in turn again. After just a few hits from POP! the stone cracked as requested. So simple and effective. The hardest part is drilling the holes with a Bosch Bulldog Extreme hammer drill. After that it's really fun!