This is a structure embodiment of“Swivel caster 1”, spherical wheel.

There are two revolution joints: vertical one between green base and glass hemisphere and slanting one between glass hemisphere and orange hemispherical wheel. Their offset distance is A. The glass hemisphere doesn’t touch the floor.

When the caster is moved and the wheel is not facing the correct direction, the offset A will cause the wheel assembly to rotate around the axis of the vertical shaft to follow behind the direction of movement.