Molds for keyboards need to be of the “superfine” quality ranking because top musicians will notice during performances when there are distortions, even if these are at a level that is impossible to detect by the naked eye.
Identifying these tiny distortions is so tough that there are very few testing technicians capable of making these judgments.
Even in Japan, there are very few companies capable of producing “superfine” quality.
One of these is Hashimoto Industry.
(The picture of the mold shows after polishing (on the left) and before polishing (on the right).)