A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders each, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft. Since each cylinder bank is essentially a straight-six which is by itself in both primary and secondary balance, a V12 is automatically in primary and secondary balance no matter which V angle is used, and therefore it needs no balance shafts. A four-stroke 12 cylinder engine has an even firing order if cylinders fire every 60° of crankshaft rotation, so a V12 with cylinder banks at a multiples of 60° (60°, 120°, or 180°) will have even firing intervals without using split crankpins. By using split crankpins or ignoring minor vibrations, any V angle is possible. The 180° configuration is usually referred to as a "flat-twelve engine" or a "boxer" although it is in reality a 180° V since the pistons can and normally do use shared crankpins.