The disk used in the experiments consists of a brass or duralumin basal part and several (0~4) brass disks set in on the basal part. There are four types of basal part, each differing in size as shown in the following image. In addition, disks placed one on top of another without the base part is also used.

Appendix Fig. 4. The  basal part of the disk. Four types of basal parts are made from a combination of diameter of 140-mm or 100-mm and materials brass or duarlumin.