Good luck finding a die to make the lefthand thread needed on one end of the turnbuckle! Buy a screen door tensioner, and modify the ends of it to make an adjustable throttle rod.
Jerry
Are you sure one is left hand thread? I thought they were both right hand thread so that if you look at either end of the turnbuckle, turning counter-clockwise (widdershins) the rod would be pulled into the turnbuckle?