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Limits, fits and tolerances

Two extreme permissible sizes of a part between which the actual size is contained are called limits.

1. Limits:

3. Tolerance

The total amount a dimension or feature is permitted to vary. The tolerance is the difference between the maximum and minimum limits.

  1. Unilateral Tolerance (One Side)

2. Bilateral Tolerances (Two Side)

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Types of fit :

  1. Clearance Fit: The hole is larger than the shaft, enabling the two parts to slide and / or rotate when assembled.
  2. Transition / Location Fit: The hole is fractionally smaller than the shaft and mild force is required to assemble / disassemble.
  3. Interference Fit : The hole is smaller than the shaft and high force and / or heat is required to assemble / disassemble.

A fit refers to the clearance between two mating parts.

3. Fit

Basic Hole System: A basic hole system is a system of fits in which the design size of the

hole is the basic size and the allowance, if any, is applied to the shaft.

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Basic Shaft System: A basic shaft system is a system of fits in which the design size of the

shaft is the basic size and the allowance, if any, is applied to the hole.

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Preferred Hole Basis Fits

Preferred Shaft Basis Fits

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Hole Basis Metric Clearance Fits

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Shaft Basis Metric Clearance Fits

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Hole Basis Metric Clearance Fits

The size of Hole to maintain – 10.000 to 10.090 (Tol. 0.090)

The size of shaft to maintain - 9.830 to 9.920 (Tol. 0.090)

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Fit allowance is 0.080 to 0.260mm

Hole Basis + Clearance Fits + Loose Running (H11/C11)

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Shaft Basis Metric Clearance Fits

Shaft Basis + Clearance Fits + Loose Running (C11/h11)

The size of Hole to maintain – 10.080 to 10.170 (Tol. 0.090)

The size of shaft to maintain - 9.910 to 10.000 (Tol. 0.090)

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Fit allowance is 0.80 to 0.260mm