After World War II, American GIs brought this Mercator knife back to America with them. There it became famous under the name "Black Cat Knife" and still has a cult following. The embossing is stamped in under a press and painted by hand after powder coating the handle. The blade of this knife is carbon steel and lockable.

The knife’s name K55K originated from "K" for Kaufmann (the original manufacturer), "55" for Hochstraße 55 (the original company address) and "K" for the cat (Katze) symbol.

OTTER knives have been manufactured and sharpened in Solingen, Germany, since 1840, using traditional methods of meticulous handcraftsmanship.