A series of locating pins can take the place of a locating plug. The pins are positioned at three points, 120 degrees apart, around the internal diameter of the hole. This arrangement is usually much more economical than making a custom plug.
Foolproofing prevents improper loading of a workpiece. The problem is most prevalent with parts that are symmetrical or located concentrically. The simplest way to foolproof a workholder is to position one or two pins in a location that ensures correct orientation.