Coupling for connecting construction parts , comprising a female coupling part and a male coupling part for placing in the female coupling part , the female coupling part comprising: - a receiving part which is at least partially tubular and comprises at its outer end an insertion opening for receiving the male coupling part in the tubular portion, wherein at least one through-opening is provided in the wall of the tubular portion of the receiving part ; - a ball which is placed in the at least one through-opening and which is movable in radial direction of the receiving part ; and - a locking sleeve which is screwed onto the receiving part and encloses the receiving part , wherein by being screwed the locking sleeve is movable relative to the receiving part in the longitudinal direction of the receiving part between an opened position, in which the locking sleeve allows a movement of the ball in the at least one through-opening in a direction away from the longitudinal axis of the receiving part for the purpose of placing the male coupling part into the receiving part or removing it from the receiving part during use, and a closed position in which the locking sleeve presses the at least one ball in the direction of the longitudinal axis of the receiving part for the purpose of locking the male coupling part in the female coupling part with the at least one ball during use, characterized in that the male coupling part is embodied as an elongate pin which comprises in its outer wall a groove for receiving the at least one ball and wherein the receiving part is provided with a closing element arranged to close off at least a part of the tubular part when in the opened position of the locking sleeve no male coupling part is placed in the female coupling part . - a receiving part which is at least partially tubular and comprises at its outer end an insertion opening for receiving the male coupling part in the tubular portion, wherein at least one through-opening is provided in the wall of the tubular portion of the receiving part ; - a ball which is placed in the at least one through-opening and which is movable in radial direction of the receiving part ; and - a locking sleeve which is screwed onto the receiving part and encloses the receiving part , wherein by being screwed the locking sleeve is movable relative to the receiving part in the longitudinal direction of the receiving part between an opened position, in which the locking sleeve allows a movement of the ball in the at least one through-opening in a direction away from the longitudinal axis of the receiving part for the purpose of placing the male coupling part into the receiving part or removing it from the receiving part during use, and a closed position in which the locking sleeve presses the at least one ball in the direction of the longitudinal axis of the receiving part for the purpose of locking the male coupling part in the female coupling part with the at least one ball during use, characterized in that the male coupling part is embodied as an elongate pin which comprises in its outer wall a groove for receiving the at least one ball and wherein the receiving part is provided with a closing element arranged to close off at least a part of the tubular part when in the opened position of the locking sleeve no male coupling part is placed in the female coupling part . <EOS>