Current position tolerance standards treat noncircular shapes (square holes, slots, keyways) either as special applications, or in a different manner than round features are treated. The Boundary Concept enables position tolerance to be applied in a consistent manner to all feature shapes by defining position tolerance as the interaction of a surface (the feature) and a boundary. Good correlation with the functional gaging practices of the automotive and aircraft industries is achieved. Drastic changes in current standards have been avoided.
The Boundary Concept is the result of a project of the SAE Drawing Standards Committee.