Another illustration of a means for avoiding close tolerances in matching component dimensions (A). The assembly (a) requires matching the length of the pin to the combined width of the links. In (b) the addition of a shim and bushing (insert) eliminate the need for the matching of part dimensions.

The use of shims for tapered gears (a) or eyebolts (b) represents one solution for the problem of controlling the dimension "n" within definite limits, including the case in which the angular orientation of the eye (b) is specified.

(b) Design Changes Which Avoid The Need For Close Tolerances

When possible, avoid using countersunk screws for fastening (a). Any lateral (e.g. center-distance) or angular misalignment stresses the screw and changes Its height relative to the part surface. Square-shouldered heads located in oversize counterbores (b) are preferable.

Tolerances on assemblies involving dowel pins can be loosened substantially by the use of roll pins (b) or groove pins.

In the case of a flywheel-and-shaft assembly in which two bushings constrain the axial position of the flywheel, a groove pin (b) eliminates the need for a two-diameter shaft, which would be needed to facilitate assembly in case (a).