ANSI Preferred Shaft Basis Fits (ANSI B4.2-1978(R1984))

The Preferred basic shaft system can be used for shafts that are manufactured in standard sizes.

ANSI Preferred Hole Basis Fits (ANSI B4.2-1978(R1984))

The Preferred basic hole system is used to apply tolerances for holes. The minimum hole is assigned the basic bore (basic size) from which the tolerance and allowance are applied. This system is widely used in industry due to standard reamers being used to produce holes, and standard size "GO GAUGES" used to check hole sizes accurately.