Table 8 - Ten Preferred Hole and Shaft Basis Fits

Preferred Fits (ANSI B4.2)

The ANSI standard and software have ten preferred hole and shaft basis fits ranging from LOOSE RUNNING to FORCE fits as shown in TABLE 8. It is recommended you use hole basis fits in most applications since it helps you reduce the cost of cutting tools and gages. However, it may be to your advantage to use shaft basis fits where you have a standard shaft size in a machine with bearings, couplings, sprockets, gears, and other components attached to it. Examples include knitting, printing, and farm machines. Each preferred fit has the same clearance or interference for hole or shaft basis fit listed on the same line. The UK and Australian standards shown above also have ten hole and shaft basis fits, but the fit H9/d9 and D9/h9 has replaced the H9/d10 and D10/h9. Input from the automotive industries in USA demanded we add the interference fit H7/u6 and U7/h6 to the ANSI B4.2 standard. We combined two clearance fits into one, and ended up with the ten Preferred Fits as shown below but with the same hole (H11, H9, H8 and H7) and shaft (h11, h9, h7 and h6) tolerance zones: