Design features quick-release knobs on all four corners for fast, easy adjustments. Corners tighten independently, so you can add pressure wherever it is needed! With 45-1/2" max. opening capacity.This 20 pc. kit includes (8) 1/4" x 20 threaded rods,(4) Quick release threaded nuts, (4) Threaded connector nuts, and (4) Right angle corners. Features: Quick-release threaded nuts on all four corners Fast, easy adjustments Corners tighten independently, so you can add pressure wherever it is needed