The position of installing a component is determined by using two dowel pins. It is better that the two dowel pins are as far apart as possible. Let us explain referring to Fig. 1. One should be aware that there is always a machining error in the positions of the holes machined in the plates. Therefore, when one point is taken as the reference, assuming that the machining error is the same and comparing the case when the position of the other hole is near with the case when it is far, the effect of the error is large when the other hole is near. From this, the accuracy is better when the spacing between the dowel pins is large.
In addition, if the positions of the two dowel pins are symmetrical, it will be possible to fix the part even if it has been reversed leading to the wrong installation of the component. In order to avoid such situations, always make it a point to ensure that the positions of the two holes are asymmetrical. Making it impossible to assemble in the reversed position is called fool-proofing.

Fig. 2 shows the relationship between the dowel pin and the depth of the hole. When machining a dowel hole in a thick plate, etc., the limit is three times the diameter. A hole deeper than this is not desirable in terms of both accuracy and economy.

Fig. 3 shows the positioning of small components. The position is determined by two dowel pins, and the fixing is done by one screw.

In the case of components that are mounted on a plate such as a guide plate, the maintenance of dies becomes easy if they are made easy to disassemble as shown in Fig. 4. Since the function is not affected much even if components such as guide plates, etc., are shifted slightly, instead of removing the dowel pins by hitting, the design is made so that they can be detached easily by making the hole in the installing plate slightly larger.