Geoffkait, you can see the Hitachi FineMet webpage easily, but buying them is hit or miss now. I think they are basically made for the military. But you can find them on Ebay occasionally.
There is the promise soon of access to some of the many sizes through a Japanese company. Right now, this company is focusing on manufacturers. I now have pigtails using two sizes for use with powercords. One has only a 1.7 mm inside diameter and the other is about 5/8 inch. The gauge of wire that can be used with the small ones means these power cords probably shouldn't be used on amplifiers.