# Can ISO GPS and ASME Torancing Systems Define the Same Functional Requirements?
## 2 From ASME Y14.5 Specifications to the ISO GPS System Drawing
The datum system A 1 B 1 C constrains all 6 degrees of freedom, so these four tolerance zones are locked (Figure 15b). The position tolerance T = 0.05 mm with respect to the datum system A 1 B due to ASME Y14.5's default simultaneous requirement defines the next set of four cylindrical tolerance zones of diameter 0.05 mm with axes defined as edges of the rectangular prism with the rectangle base 24 mm \(\times\) 18 mm. So, the requirement for the relative location between the axes of the four holes is tightened. The datum B in the datum system A 1 B constrains only the orientation of the axes of the four holes. Theoretically, exact linear dimensions apply only between the holes but do not apply to datum B--the linear theoretically exact dimension of 12 mm is not considered. The pattern of four holes may float up and down with respect to the datum B, but the pattern cannot rotate with respect to the datum B. The axes of the four holes shall be within the largest tolerance zones and the smaller tolerance zones simultaneously, as is shown in Figure 15b. The ISO GPS system does not use the concept of composite tolerance. The function depicted by the meaning in Figure 15b is secured by stacked two-level tolerance indications (Figure 16). The upper tolerance indicator is identical, as in Figure 14, and in the lower tolerance indicator the modifier \(><\) (_for orientation constraint only_) is specified after the datum B. The modifier \(><\) indicates that datum the B establishes only orientation for the pattern of tolerance zones of diameter T = 0.05 mm. As it was explained for the indication in Figure 14, modifier CZ is specified after the tolerance value T = 0.05 to override the ISO GPS system default independency principle to create the pattern of the four holes and the encircled X indicates that the axes of maximum inscribed cylinders shall be contained as the tolerance features in both tolerance zone patterns. Figure 3:4 The ISO GPS system specification equivalent to the requirement given in Figure 13a. The position tolerances in Figures 13a and 15a are locating axes of the holes. According to ASME Y14.5, the axis of the hole is derived by using the actual mating envelope, which contacts the highest points of the hole surface (axis of the maximum inscribed cylinder). Figure 3:5 The ISO GPS system specification equivalent to the requirement given in Figure 15a. Figure 3:6 (**a**) Position tolerance T = 0.15 mm locates the pattern with respect to datum system A\(\,\)B\(\,\)C, position tolerance T = 0.05 mm refines mutual location between holes and limits rotation of the pattern with respect to the datum system A\(\,\)B (ASME Y14.5); (**b**) tolerance zones—meaning of two level specification. The location of the axis is often used because it is intuitive and easy to explain. In an assembly, from the functional point of view, the surfaces of holes and pins come into contact with the mating part. This may be well observed when a functional gauge is used to verify specified position tolerances. The hole axis is not located, but a hole surface must not violate the maximum material virtual condition boundary. The difference in the axis and surface interpretation is usually negligible. The problem may occur when a hole is significantly out of cylindricity and only the axis of such a hole is controlled. To get rid of the mentioned problem, _maximum material requirement_ (MMR), marked by the encircled M [13, 27], is specified. It should be mentioned that the new edition of ISO 2962 [27] was just published (June 2021). According to ASME Y14.5, five holes in the plate (Figure 17a) shall be considered as a pattern and all tolerances apply simultaneously. The hole locations shall be verified in one attempt by material gauge: a close-end slot with four pins of diameter equal to maximum material virtual size MMVS = 7.7 mm [27] and one pin of diameter MMVS = 9.6 mm (Figure 17b) located with respect to the datum system A \(|\) B\(|\) C. The plate during verification shall lay on the slot bottom that establishes the datum A.