Wooden clamps to clamp wood. Specifically, shop-made hand screws. Dimensions and materials are not important, however I will give some as a starting point. Do not use pine nor poplar. Quarter-inch threaded rod will work. Hardware is available at Lowes, or Home Depot.
Note on holes: Tee nuts must be a snug fit. Rod holes must be a loose fit. Handle holes should be snug and the rods threaded in. Nail holes must be snug, with rod flats up for drilling. Lightly peen nails. A drop of cyano glue might be used for snug fits. Tee nuts are of the type with holes around the rim, no teeth. Large dowels may substitute for turned handles. Use tap-tap, tap to enlarge drawing. Making hand screws is a good winter activity. Groups of three is convenient.
