Upon Mr. Meier's request I shall explain slug embossing a little better to help others learn what slug embossing is.

Slug embossing was used to remove old embossing on an insulator. The old embossing was ground off and to do so more of the metal of the mold had to be removed around the embossing as well. The new embossing was then embossing inside the "band" aka slug plate.