US Patent 9021761 Building unit with mating sides

A building unit including upper and lower surfaces, and a plurality of side surfaces extending between the upper and lower surfaces defining a generally trapezoidal shape in plan view. The unit includes a first pair of the side surfaces, located on opposite sides of the unit and extending non-linearly and generally obliquely with respect to each other in plan view, where each side surface of the first pair has a midpoint bisecting it into two portions. The portions on each side of the midpoint are a 180° rotational image of the other portion about the midpoint. One side surface of the first pair is longer than the other, and the longer side surface includes a midsection of the same length and configuration as the other, shorter side surface. Each of the shorter and longer side surfaces interlocks with either the shorter or longer side surface of another like building unit.