ANSI PREFERRED TOLERANCES AND FITS CHARTS


Preferred tolerances and fits given in ANSI B4.1-1967 (R2004) standard are summarized in the following charts. For the calculations of ANSI limits, fits and tolerances, visit ANSI limits and fits calculator.

Running and Sliding Fits [RC]: Intended to provide a similar running performance, with suitable lubrication allowance, through out the range of sizes. The clearances for the first two classes, used chiefly as slide fits, increase more slowly with diameter than the other classes, so that accurate location is maintained even at the expense of free relative motion.



Fit Detail Description Symbol
Close sliding fits [RC1] Intended for the accurate location of parts which must assemble without perceptible play. H5-g4
Sliding fits [RC2] Intended for accurate location of parts but with greater maximum clearance than class RC 1. Parts made to this fit move and turn easily but are not intended to run freely, and in the larger sizes may seize with small temperature changes. H6-g5
Precision running fits [RC3] The closest fits which can be expected to run freely, and are intended for precision work at slow speeds and light journal pressures, but are not suitable where appreciable temperature differences are likely to be encountered. H7-f6
Close running fits [RC4] Intended mainly for running fits on accurate machinery with moderate surface speeds and journal pressures, where accurate location and minimum play is desired. H8-f7
Medium running fits [RC5]-[RC6] Intended for higher running speeds, or heavy journal pressures. H8-e7
H9-e8
Free running fits [RC7] Intended for use where accuracy is not essential, or where large temperature variations are likely to be encountered, or under both of these conditions. H9-d8
Loose running fits [RC8]-[RC9] Intended for use where wide commercial tolerances may be necessary, together with an allowance, on the external member. H10-c9
H11-

Note: There is no symbol in the standard for the shaft tolerance of RC9.

Locational clearance fits [LC]: Intended for parts which are normally stationary, but which can be freely assembled or disassembled. They run from snug fits for parts requiring accuracy of location, through the medium clearance fits for parts such as ball, race and housing, to the looser fastener fits where freedom

Fit LC 1 LC 2 LC 3 LC 4 LC 5 LC 6 LC 7 LC 8 LC 9 LC 10 LC 11
Symbol H6-h5 H7-h6 H8-h7 H10-h9 H7-g6 H9-f8 H10-e9 H10-d9 H11-c10 H12- H13-

Note: There are no symbols in the standard for the shaft tolerances of LC10 and LC11.

Locational transition fits [LT] : A compromise between clearance and interference fits, for application where accuracy of location is important, but either a small amount of clearance or interference is permissible.

Fit LT 1 LT 2 LT 3 LT 4 LT 5 LT 6
Symbol H7-js6 H8-js7 H7-k6 H8-k7 H7-n6 H7-n7

Locational interference fits [LN] : are used where accuracy of location is of prime importance and for parts requiring rigidity and alignment with no special requirements for bore pressure. Such fits are not intended for parts designed to transmit frictional loads from one part to another by virtue of the tightness of fit, as these conditions are covered by force fits.

Fit LN 1 LN 2 LN 3
Symbol H6-n5 H7-p6 H7-r6

Force Fits [FN] : Force or shrink fits constitute a special type of interference fit, normally characterized by maintenance of constant bore pressures throughout the range of sizes . The interference therefore varies almost directly with diameter, and the difference between its minimum and maximum value is small to maintain the resulting pressures within reasonable limits.

Fit Detail Description Symbol
Light drive fits [FN1]: Fits requiring light assembly pressures and produce more or less permanent assemblies. They are suitable for thin sections or long fits, or in cast-iron external members. H6-
Medium drive fits [FN2] Suitable for ordinary steel parts or for shrink fits on light sections. They are about the tightest fits that can be used with high-grade cast-iron external members. H7-s6
Heavy drive fits [FN3]: Suitable for heavier steel parts or for shrink fits in medium sections. H7-t6
Force fits [FN4]-[FN5]: Suitable for parts which can be highly stressed or for shrink fits where the heavy pressing forces required are impractical. H7-u6
H8-x7

Note: There is no symbol in the standard for the shaft tolerance of FN1.

Reference:

  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc.
  • ANSI/ASME B4.1 - 1967 (R2004) Preferred Limits and Fits for Cylindrical Parts