The chainrings and pedals attach to the cranks. The most common tandem crankset is a set of four cranks. Biopace chainrings have a reduced chainring diameter coinciding with the cranks being horizontal. In typical modern bikes, the bottom bracket spindle is separate from the cranks. Some eccentrics are pejoratively considered "cranks" rather than geniuses. Fully counterweighted stroke and even stroke cranks can be bought from aftermarket companies. The Tandem Twin is where the cylinders are longitudinal, and have two cranks geared together. Some manufacturers make cranks and bottom brackets to both specifications. With a hurdy-gurdy, the musician cranks a wheel whose rosined edge touches the strings. The suspension is by torsion bars and cranks. Early submarines were mounted with spars and powered by hand cranks. Bee cranks (Killer cranks) and diesel conversion heads. Many of the earliest ones operated by turning large cranks. Operators moved the beams using cranks and wires. Combined with the length of the cranks, it determines the bicycle's ground clearance.