What is the H7/h6 fit clearance?
2 Answers
H7/h6 is a hole-basis system fit clearance. H7/h6 is a tolerance fit designation for mechanical components in the industry. H7 refers to the tolerance zone designation of the hole it fits with, while h6 represents the tolerance zone designation of the outer surface of the bearing (where the bearing acts as the shaft when fitting with the hole). Below is more information about the clearance: 1. The function of the clearance includes storing lubricating oil, compensating for various errors, etc. Its size affects the relative motion between the hole and the shaft. 2. Clearance fits are mainly used for movable connections between holes and shafts, such as the connection between sliding bearings and shafts. Concept of fit tolerance: Fit tolerance refers to the sum of the tolerance zones of the shaft and hole that form the fit. It is the allowable variation in clearance or interference, and its size indicates the range of variation in the tightness of the fit. It is an important comprehensive indicator for evaluating the quality of the fit.
From a mechanical design perspective, the H7/h6 fit is a common clearance fit within ISO standard tolerances. Here, 'H' indicates the hole's tolerance zone starts from the basic size with positive deviation upwards, while 'h' denotes the shaft's tolerance zone begins from the basic size with negative deviation downwards, combining to form a slight clearance fit. This means the actual hole size is always slightly larger than the shaft, providing a small gap that allows parts to slide or move freely during assembly without being too loose and causing wobble. In automotive applications, this fit is widely used in bearing mounting points or piston pin holes to accommodate thermal expansion and lubrication needs. For example, during engine operation, a slight clearance reduces friction and wear as the piston moves up and down. However, excessive clearance may lead to part loosening and noise, while insufficient clearance can cause jamming and failure. Thus, selecting the appropriate clearance fit is crucial and must be calculated based on working conditions and materials. In my daily design work, I often refer to manuals to choose suitable tolerances, avoiding assembly issues.
