The Mercator K55K is of very simple construction: The handle consists of a folded piece ofsheet metal, usually painted black, engraved with the outline of a leaping cat and the legend "K55K", with the second "K" being backwards. The blade has anail-nickby which it may be grasped to pull it open, and it locks in the open position (alockbackknife), after which it may only be closed by depressing a lever at the back of the knife. As of 2013, the knife can be purchased with a stainless steel or carbon steel blade.
The Mercator's construction is similar to that of the FrenchDouk-Doukknife, in terms of the simple folded-metal handle. However, the Douk-Douk is aslipjointknife, whereas the K55K is alockbackknife and has a different blade geometry.