These wheels were 40" but there are no rules. Any size can be made to work depending on the look you want. Smaller wheels will likely look better spaced a bit closer. For stability, the wheels were cut as half wheels and braced across the base diameter with screwed metal strips. Holes in the flat metal allowed stakes to be driven into the ground deeply. The metal also served to protect the wood from rotting. Coating with oil or stain will help extend the life of the wooden wheels.