Differences in the main journal and crank pin circumference occur from unevenness in manufacturing precision. For that reason, there are several standard sizes for the main journal and crank pin. This size code is inscribed on the crankshaft. There are engines where there is only one size, in which case they do not have the size code inscribed. Use this code when selecting bearings to prevent the crankshaft main journal oil clearance precision or connecting rod oil clearance precision in order to prevent abnormal noise and seizing and to maintain good fuel economy. As the size code increases, the diameter of the main journal and crank pin decreases in micron units. Number of standard sizes, size coding and location of inscription differ according to the engine models.