ISO System of Limits and Fits

ISOTOLTM Computer Tolerance Software ISBN 0-9744477-1-4


Preferred metric sizes, fits, and tolerance zones for holes (H11, H9, H8, H7) and shafts (h11, h9, h7, h6) 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 ISOTOLTM* 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 (ISOTOLTM) in your business, which has been successfully used around the world for 70 years and saved billions of dollars in manufacturing and engineering. For nearly two years a free online version of the ISOTOLTM has been available. The online version was not intended to help design a metric fit, but to interpret an existing metric fit and convert it to inches. New online versions will be available later this year.

NOTE*:  The online version of the ISOTOLTM will not be available until later this year. ISO System of Limits and Fits coded limits may be calculaded  from tables in the METRIC STANDARDS for Worldwide Manufacturing electronic or hardcover editions or from the tables in Chapter 6. You may want to purchase the first edition of the software stored on an ISOTOLTM CD.

  Order your copy of ISOTOLTM Metric Limits Software today! 



The ISO System of Limits and Fits is a highly successful tolerance system to help cut costs in manufacturing and engineering.  Germany has taken the lead in this area, and it has helped cut cost of engineering time, material stock (see h11, h9, h7, h6), cutting tools and gages.  GO/NOGO gages held to these tolerances are readily available in Germany and most other countries. The American National Standard ASME B4.2 cover the preferred metric sizes, preferred tolerance zones and the ten preferred hole or shaft basis fits used throughout the world. You have had free access to the online version of the ISOTOLTM software for nearly two years.  This free service has ended, and please contact me for future options. The site GOmetricUSA.org, still provides free interpretations of all tolerance zones with metric limit dimensions for sizes in the ISO system. You may want to use the ISO system here, and it is a powerful rationalization tool.    

Preferred Fit  ; Simply click on one of the ten proven fits . If you decide to use a different hole or shaft tolerance, you can increase or reduce the clearance by just a click on one of the 150 other tolerance zones.   Each time the new fit condition is instantly displayed.    You can modify the fit,   and still specify one of the first choice tolerance zones for holes (H11, H9, H8, H7) or shafts (h11, h9, h7, h6 ) which produce the largest cost reductions in gages,  material stock and tooling.  The ASME B32.100-2005 material standard and other national standards for cold finished steel rod material specify the four (4) preferred shaft tolerances h11, h9, h7, and h6 in all the largest industrial countries of the world.  

Preferred Metric Sizes ; Click on first, second or third choice metric size or enter your own special size up to 500 mm.  

You may also click on a preferred inch size or enter a special size followed by the inch (") symbol.

Output ;   Instant display of limit dimensions for hole, shaft and fit.

For example;
   25H11/c11 (hole 25.130/25.000; shaft 24.890/24.760; fit 0.370/0.110)

Press Copy in order to transfer the above line to drawing or specification.

This page provides a description of the ISO System of Limits and Fits.  You may want to see How It All Started. More useful information is published on the first web site, www.kok.com, that was first on the Internet 20 years ago.

See Chapter 6 of the book METRIC STANDARDS for Worldwide Manufacturing for complete details about the preferred metric limits and fits (ANSI B4.2).

Users Quotes

1.  I think the ISOTOLTM software is an excellent tool  for analyzing and harmonizing fits and tolerances of metric and inch designs.  It's a real timesaver because it minimizes errors when looking up numbers repeatedly in the ISO tables.   Mike E Yamat myamat at cooperpower.com; Phone 414 768 8303; Fax 414 768 8236 (User of metric book and software) Cooper Power Systems, 2800 9th Ave, S Milwaukee WI 53172

2. Rick wrote the following about the computer program; "ISOTOLTM interfaces just fine with AutoCAD. The software works just fine with all MS Windows versions and MDT. It is straight forward and easy to use. It is a simple program that would be of great value to anyone that needs to figure tolerancing".  Rick Novara ricknovara at compuserve.com; Phone 704 921 0303; Fax 704 921 0304, Novara Engineering, 12325 Mallard Ridge Drive, Charlotte NC 28269.