Translations for pocketknife in French

Here are paragraphs from public domain books translated:
Grimaudan glanced around to see if anyone were looking. Some tram- cars and pedestrians were passing. But, bah, they will not suspect anything. He opened his pocketknife and thrust it between the twelfth and thirteenth stones. Grimaudan regarda autour de lui. Des tramways passaient, des gens passaient. Mais bah ! qui pouvait se douter ?… Il ouvrit son canif et le planta entre le douzième et le treizième pavé.
The Extraordinary Adventures of Arsene Lupin, Gentleman Burglar, by Maurice Leblanc Arsène Lupin gentleman-cambrioleur, de Maurice Leblanc