Positional tolerances of threaded holes and through-holes for fixed fasteners (Figs 6.10 and 7.1) are usually calculated from the maximum diameter of the bolt and the minimum diameter of the through-hole (see 6.7).

Figure 7.1: Positional tolerance of a threaded hole

A prerequisite for these calculations is that the axis is perpendicular to the joint surface. In the extreme case (Fig. 7.2) the parts still fit.

Figure 7.2: Positional tolerance zones of threaded hole and through-hole

When the axis of the threaded hole deviates from the perpendicular orientation (but remains in the positional tolerance zone) the parts do not fit (Fig. 7.3).

Figure 7.3: Orientation deviations taking advantage of the positional tolerance zones

However, when the positional tolerance zone is located outside the part and applies to the external projection of the feature (axis) (Fig. 7.4), the part fits in any case (Fig. 7.5). The external projection has the length of the through-hole in the case of head screws (Fig. 7.6), and the length of the outstanding part of the stud or dowel pin (Fig. 7.7). The projected tolerance zone applies only to these lengths, not to the (length of the) axis within the workpiece.

Figure 7.4: Projected tolerance zone

Figure 7.5: Taking advantage of the positional zone by inclined axes

Figure 7.6: Projected tolerance zone for threaded hole and head screw

Figure 7.7: Projected tolerance zone for threaded hole and stud or for hole and pin

ISO 10 578 defines the projected tolerance zone as follows. The projected (positional)...