Turnbuckle

A turnbuckle (also called a rigging screw or bottle screw) is a mechanical tensioning device consisting of a central barrel threaded at each end in opposite directions, allowing tightening of a connected rod or wire when the barrel is rotated. In cargo securing, turnbuckles are connected at the lower end of lashing rods or wire lashings to apply and maintain tension in the securing arrangement. ISO and ASTM standards govern turnbuckle dimensions and minimum breaking loads; the CSS Code and the Cargo Securing Manual specify the allowable loading for each type in the securing assessment. The chief mate selects turnbuckles based on the required MSL for each lashing position. After lashing rods are hooked to the container corner castings, the OOW or bosun's crew tightens the turnbuckles with a lashing bar to the pre-tension level specified in the Cargo Securing Manual—typically sufficient to take up any slack without over-stressing the corner casting. Turnbuckles must be inspected for corrosion, thread wear, and distortion before use; a seized barrel or stripped thread that prevents proper tensioning compromises the entire lashing. Regular inspection of turnbuckles and retightening after the first day at sea, when initial settlements occur, is standard practice on container vessels.