The crankshaft part that connects to the connecting rod is the crankpin.
A crankpin is the offset section of a crankshaft attached to the connecting rod’s larger, or “big,” end. As the crankshaft rotates, the crankpin follows a circular path around the crankshaft’s main axis. The connecting rod turns that motion into the piston’s up-and-down movement inside the cylinder.
The crankpin’s cylindrical surface acts as a journal for the connecting-rod bearing. In most modern car engines, that bearing is a replaceable plain bearing, although bushings and roller bearings are also used in some designs. The crankpin is sometimes called a rod-bearing journal, which can cause confusion with the crankshaft’s main journals. Main journals support the crankshaft in the engine block; crankpins connect to the rods.
Engine layouts affect crankpin use. In many V engines, one crankpin is shared by a pair of cylinders, while straight and flat engines commonly use one crankpin per cylinder. The distance between the crankshaft centre and crankpin centre is the crank throw radius, and twice that distance contributes to piston stroke.