Tolerances include dimensional tolerance, shape tolerance, position tolerance, etc.
1. dimension tolerance: refers to the variation of allowable dimension, which is equal to the absolute value of the algebraic difference between the maximum limit dimension and the minimum limit dimension.
2. shape tolerance: refers to the total allowable variation of the shape of a single actual element, including 6 items: straightness, flatness, roundness, cylindricity, line profile and surface profile.
3. positional tolerance: refers to the total allowable variation of the position of the associated actual element to the benchmark. It limits the mutual positional relationship between two or more points, lines and surfaces of the part, including 8 items: parallelism, verticality, inclination, coaxiality, symmetry, positional degree, circular jump and full jump. Tolerance represents the manufacturing accuracy requirements of parts and reflects the degree of difficulty in machining. The tolerance level is divided into 20 levels: IT01, IT0, IT1,..., IT18. The level is reduced in turn, and the tolerance value is increased in turn. It means international tolerance.
