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.
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.

