Crankhd -

: In this design, the spindle is permanently attached to one of the crank arms (usually the drive side), simplifying installation and increasing stiffness. Engine Crankshafts

: The most standard modern setup, consisting of a left arm, a right arm, and a separate spindle . They typically use square-taper or splined (like Shimano Octalink) interfaces. CrankHD

A bicycle crank is the lever that connects the pedals to the bottom bracket, turning your pedaling effort into rotational motion to drive the chain. : In this design, the spindle is permanently

: Common on older American-made bikes and children's BMX bikes. A single piece of forged steel forms both arms and the axle. A bicycle crank is the lever that connects

In internal combustion engines, the crankshaft is the "backbone" that converts linear piston motion into rotary motion to drive the wheels.