What is the best material to put under a swing set?

Common materials and tools required to install a swing set are as follows: - 4x4 treated posts, 8 feet in length - 2x6 treated lumber, 12 feet in length - galvanized nails - 3/8 inch galvanized chain - S hooks - a drill - level - hammer

You will need the following materials in order to install a swing set: -4x4 pressure treated posts -4x6 pressure treated beam -galvanized pipe straps -8 galvanized lag bolts -2 galvanized U bolts -monkey bars/ladder/swings/rings The following tools are also required: -post hole digger -level -tape measure -hammer -chisel -saw (either hand or power) -(optional) drill