Table 5 & 6 - Preferred Tolerance Zones

Preferred Tolerance Zones

The ISO tolerance zones shown here are those specified in the ANSI B4.2 standard and tabulated in the reference material. Those shown in the green areas are those used in the preferred fits.

The ISO System of Limits and Fits has been in use in many countries for more than 70 years. Cold finished round bars held to the tolerance zones, h11, h9, h7 and h6, are covered in national standards throughout the world as shown in TABLE 7. GO-NOGO gages to inspect parts and reamers to produce the holes to these tolerance zones are frequently readily available. Designed software where you can enter metric or inch fit conditions, and compare them with a proven fit, has been available since 1997. A second online version was available for two years, and a new third online version will be released soon.


The ISO System of Limits and Fits offer industries in USA numerous savings opportunities. The required documentations to help cut costs in terms of engineering time, tooling and material stock has been prepared, and it is up to us to take advantage of the system. The software program, ISOTOLTM, make the limit dimensions quick to calculate and copy without errors, and can maximize those opportunities while saving time. Preferred Sizes and tolerances help reduce the number of different hole and shaft sizes used in products.

























Hole basis fits with hole tolerances H11, H9, H8 and H7 help rationalize on standard cutting tools and gages, whereas shaft basis fits with shaft tolerances h11, h9, h7 and h6 help rationalize on standard round steel bars available in all major industrial countries. The ANSI B32.100 standard specify the above shaft tolerances and diameters, and the sizes are according to those shown in TABLE 1. How the tolerance zones apply in national standards are shown in TABLE 7.