The granat obronny wz. 33 (Polish for defensive grenade, mark 33) was a fragmentation grenade used by the Polish Army before and during World War II. The shell casing was molded from cast iron and formed into a pineapple-shaped oval, typical of World War II-era hand grenades. More specifically it was modelled after earlier Polish grenades of 1920's (such as the Defensive grenade wz.24), which in turn were based on French World War I F1 grenade. It was fitted with wz.Gr.31 percussion fuse. To increase reliability, the grenade had two blasting caps and two strikers. The casing was produced in one of three factories, a letter on the casing denoting the producer (K for Końskie, M for Warsaw and W for Wilno).