Tolerances are needed in manufacturing because it is impossible to maintain perfect accuracy in dimensions. Small variations in tolerances, such as 0.004 inches for a shaft diameter, can cause parts to not fit together properly. The case study describes a situation where a shaft was manufactured 0.004 inches larger than the specified diameter, preventing it from fitting the bearing. Tolerances should be specified at the design stage to avoid wasted time and money fixing misfit parts later on. Fits between parts can be clearance, interference, or transition fits depending on the tolerances. Geometric tolerances also need to be specified to control the shape and relative positions of surfaces, such as flatness, straightness, and parallelism. Examples