Hole-spacing deviation depends on the nature of the fit between the shaft (e.g., bolt, stud, screw, pin) and the hole. Calculations typically employ the maximum-minimum method within a dimensional chain. When calculating hole-spacing deviation, the following assumptions are generally made: the deviation in hole position depends on the magnitude of the fit clearance and the connection method, rather than the nominal hole spacing itself; and the dimensions of the hole and shaft are known-specifically, the minimum clearance is known. The function of the clearance is to allow the shaft to pass freely through the hole for assembly; essentially, the clearance compensates for errors in hole spacing arising during the manufacturing of the two connected parts. A distinction must be made between two types of connection structures: bolts (passing through clearance holes)-see figure below; and screws (studs, pins, rivets, etc.)-see figure below. The minimum clearance $S_M$ is defined as: $S_M = d_0 - d$, where:
$d_0$ is the minimum limiting dimension of the hole; $d$ is the maximum limiting dimension of the shaft. When there are multiple holes (more than three) arranged in a straight line, the deviation value varies depending on the dimensioning method used; calculation formulas are provided in Table 2-5-1. Dimensioning via the chain method is generally not recommended when the number of holes ($n$) exceeds three, because the deviation value decreases as the number of holes increases-meaning that the greater the number of holes, the smaller the allowable spacing deviation and the more difficult the machining process becomes. Conversely, if the stepped dimensioning method is used, the hole-spacing deviation remains independent of the number of holes. For slotted holes (fish-eye holes), countersunk holes, and similar connection holes, the hole-spacing deviation $\Delta L'$ should be calculated using the formulas in the table below.
