A waveboard or wave board or hi-tide is similar to a skateboard, but built on a riding system called a caster board. The board rides on two independently pivoting platforms, each with a one-wheel caster. Thus, each wheel is able to rotate a full 360°. The platforms are connected by a torsion bar that allows them to pivot about the X–axis. On some models, this torsion bar spins independently of the two platofrms, allowing the rider to grind across surfaces.