Many apparently 'standard' names for configurations are historic, arbitrary, or overlapping. For example, the 180° V engine is so named because the crankshaft is related to a V engine more closely than it is related to other opposed-piston engines such as the boxer. Others would consider it a flat engine because of its shape. The names W engine and rotary engine have each been used for several unconnected designs. The H-4 and H-6 engines produced by Subaru are not H engines at all, but boxer engines.