Lock for safety belts

Lock for a safety belt comprising a belt lock with spaced plates defining an insertion path, a plug-in tongue for insertion in the insertion path, a latch movable transversely to the insertion path to the locked position in which the latch is interposed in the path of the tongue and to the open position in which the latch does not block passage of the tongue in the insertion path, a manually operated pressure element to move the latch from the locked position to the open position, spring means retaining the latch in the open position when the tongue is withdrawn from the insertion path, and an insertion lock in the belt lock activated by a pulling force on the plug-in tongue exceeding a predetermined value to restrain said spring means to permit withdrawal of the tongue from the insertion path and prevent renewed insertion after such withdrawal.