Dear etaoin: I suddenly remembered the turnbuckles on my screen doors, and almost choked on the pie I was eating.
Detail about them, an elongated "O" has threaded holes aligned with axix,at each end, but the rod ends have to have one end thread right handed,and other end left hand threaded to get change in length. I also used miniature ones in my radio controlled airplanes, to adjust some of the controls.

The essential part of the parbuckle is the snaphook used to
hitch the chain around the barrel Here are some pictures of various kinds:(not as strong as the ones in the picture)
http://anyardfactory.com/lanyard-hardware-option.htm