Tolerance Limits and Fits


Reading Assignment


Iso 286


Lazy Machinist Video


Applicable standards: ANSI B4.1, ANSI B4.2, ISO 286, ISO 1829, ISO 2768, EN 20286, JIS B 0401

See: Limits and Fits, Selecting Size Tolerances (video)

Preferred ISO Fits (from ANSI B4.1)

[RC] Running Clearance Fit

  • RC1 – Close Sliding Fits
  • RC2 – Sliding Fits
  • RC3 – Precision Running Fits
  • RC4 – Close Running Fits
  • RC5 and R6 – Medium Running Fits
  • RC7 – Free Running Fits
  • RC8 and RC9 – Loose Running Fits

[LC] Clearance fit

  • LC1 – Free Running
  • LC2 – Loose Running
  • LC3 – Easy Running
  • LC4 – Sliding
  • LC5 – Close Clearance
  • LC6 – Locational Clearance
  • Through LC11

[LT] Locational Transition fit

  • Location-Slight Interference
  • Location/Transition
  • Through LT6

[LN] Locational Interference fit

  • LN1 – Location/Interference
  • LN2 – Medium Drive Fit
  • LN3- Force Fit

[FN] Force Interference

  • FN1 through FN5


Hole-Based System (Hole size is kept constant, shaft varies)

Shaft-Based System (Shaft size is kept constant, hole size varies)

Hole Tolerance Zones

Shaft Tolerance Zones

ISO Vs. ANSI System

  1. Running or sliding fits [RC]
    This includes fits with guaranteed clearances which are specified for movable couplings of those parts which have to run or slide one against the other.
  2. Locational fits [LC, LT, LN]
    This includes clearance or interference fits specified for precise locational positioning of coupled parts. The coupled parts must be fixed mechanically to prevent one moving against the other during assembly. Depending on the locational positioning of tolerance zones of the coupled parts, 3 types of these fits may be distinguished: Clearance fits [LC], interference fits [LN] and transition fits [LT].
  3. Force or shrink fits [FN]
    This includes guaranteed interference fits specified for fixed (non-demountable) couplings of parts.



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