Amico 0.39" Thread 304 Stainless Steel Closed Body Jaw Jaw Turnbuckle Rigging Bottle Screw by Amico. $16.76. Made from 304 stainless steel for maximum corrosion resistance and durability. A turnbuckle is a device for adjusting the tension or length of ropes and cables. It normally consists of two threaded eyelets. This 304 stainless steel turnbuckle features jaw and jaw ends, closed body, an ideal rigging tool.