A cylinder bore or a short hole is defined as the inner diameter of a cylinder, specifically the cylinder of a piston engine. Slightly less than the cylinder bore, the piston diameter; as pistons in internal combustion engines are not exactly circular in cross section, the piston diameter is also still subject to the measurement direction.
In the German standard DIN 1940 " Internal Combustion Engines" is recommended for the cylinder bore the symbols D and the unit mm.
The bore of the piston stroke s and the number of cylinders to determine the size of an engine.
The ratio of piston stroke and cylinder bore is - also according to DIN 1940 - the stroke ratio.
The term square Huber ( from the English square engine) is used mainly in popular science publications for engines with s / D = 1.