Too bad Trow and Holden tanks and springs are no longer sold at Revain. They had a good range of sizes. Why is size important? Because you don't need huge wedges to split smaller rocks, and therefore you don't have to drill big, deep holes that will dull your expensive drill bits and drain your batteries (for those with cordless drills). 3/8 inch wedge splits rocks over a foot deep. Visit the Trow and Holden website and read their guides to learn more. Here I will only tell you the three most important things to make these tools last longer. First drill a hole almost as deep as the wedge itself so it doesn't hit the rock and start buckling. Second, before each use of the wedges and washers, make sure they are covered with a thin layer of lubricant so the wedges slide easily. Finally, all you need is a light hammer to gently tap the wedges. Just be patient and let the wedges do their job so they don't warp the seals and last longer.