 The late 1800s saw the introduction of cheap mass-manufactured nails, and wooden boules gradually began to be covered with nails, producing "boules cloutées" ("nailed boules").After World War I, cannonball manufacturing technology was adapted to allow the manufacture of hollow, all-metal boules.The first all-metal boule, "la Boule Intégrale", was introduced in the mid-1920s by Paul Courtieu.