Abstract: An antitheft device for marking articles for sale and comprising two members, which automatically interlock one another when one member is inserted in a cavity in the other member, the first member being a rod-shaped body with a completely or partially pointed insertion end, whereby said rod-shaped body is capable of engaging for instance balls loosely arranged in the cavity of the second member, a third member of magnetizable material being inserted below the loosely arranged balls, whereby a resilient member with an upward driving force is placed below said third member. According to the invention the resilient member is an annular plastic member with inward connecting parts connected to a centrally arranged disk-shaped plastic member pressing against the third member in the cavity, the annular plastic member being secured by way of squeezing to an annular groove in the bottom of the housing.