ISO System of Limits and Fits

Computer Tolerance Software ISBN 0-9744477-1-4


Summary

Preferred metric sizes, tolerance zones for holes (H11, H9, H8, H7) and shafts (h11, h9, h7, h6) and fits are covered in the Preferred Metric Limits and Fits, ANSI B4.2 1978, standard. The purpose of this standard is to help American manufacturing to cut costs in terms of engineering time, tooling, material stock, gages, etc. The material in the and METRIC STANDARDS for Worldwide Manufacturing are based on the above standard. You may also want to introduce the ISO System of Limits and Fits () in your business, which has been successfully used around the world for 70 years and saved millions of dollars in manufacturing and engineering. Use the following material in your selection of sizes, tolerance zones and fits:

 

TABLE 1  PREFERRED SIZES (ANSI B4.2)

 

 

TABLE 2 TOLERANCE ZONES FOR HOLES (ANSI B4.2)

 

TABLE 3 TOLERANCE ZONES FOR SHAFTS (ANSI B4.2)

 

TABLE 4 PREFERRED FITS (ANSI B4.2)

 

Gages*:
Off-the-shelf GO and NOGO plug, snap and ring gages to preferred metric sizes held to the ISO 1938 standard are normally available in EU. The ISO standard is published in Chapter 7 of the electronic 2012 edition of METRIC STANDARDS for Worldwide Manufacturing. Chapter 7 in the 2007 hardcover edition of the above book and specifies gages to ANSI B4.4M (now withdrawn) for use with the ISO System of Limits and Fits in ANSI B4.2. It is in full agreement with American gaging practices where all gage makers tolerances, wear allowances, measurement uncertainties and form controls are held within the work piece limits of size.

NOTE *Complete ISO System of Limits and Fits is now stored on two CD’s, Computer Tolerance Software and Computer Software for Gages. The CD’s are now available from .

 

References:
Kverneland, Knut O: “METRIC STANDARDS for Worldwide Manufacturing” published by (ASME Press) 2012 Electronic (2007 Print) 800p 500 tables ISBN: 0974447773 (0791802612)
ANSI B4.2-1978 Preferred Metric Limits and Fits
ANSI B32.100-2005 Preferred Metric Sizes for Flat, Round, Square, Rectangular, and Hexagonal Metal Products
Slay, Matt: President, Jordan Machine Co., 355 Clow Lane, PO Box 170339, Birmingham, AL 35217, Ph: 205 849 5050
Fx: 205 849 5075, mattslay@jordanmachine.com, published the online version of