1. Physical Terms and Definitions
(1) Holes mainly refer to cylindrical inner surfaces, such as support holes, fixing holes, etc. The machine tool also includes other inner surfaces determined by a single size, such as rectangular holes, slot widths, etc.
(2) Shaft mainly refers to the cylindrical outer surface, such as shaft, pin, etc., and also includes other outer surfaces determined by a single size, such as key width, key thickness, etc.
2. Terms and Definitions Related to Dimensions
(l) Dimensions are numbers that express length values in specific units (eg mm).
(2) The nominal size given in the basic size design is called the basic size, which determines the size of each part of the part.The basic size of the hole is indicated with an uppercase "D"; the basic size of the shaft is indicated with a lowercase "d".
(3) The size of a hole or shaft obtained by measuring the actual size of the part after machining.
(4) The limit size allows the two limit values of the basic size change, collectively referred to as the limit size. The larger one is called the maximum limit size, and the smaller one is called the minimum limit size, and they are all determined based on the basic size.