Metric Tolerances
Basic Hole and Basic Shaft Systems
Metric limits and fits are divided into two different systems; the basic hole system and the basic shaft system.
Basic hole system: The basic hole system is used when you want the basic size to be attached to the hole dimension. For example, if you want to tolerance a shaft based on a hole produced by a standard drill, reamer, broach, or another standard tool.
Basic shaft system: The basic shaft system is used when you want the basic size to be attached to the shaft dimension. For example, if you want to tolerance a hole based on the size of a purchased standard drill rod.