The thumb screws look like hose clamps from the mid 70's. The thumb screw is a worm gear that acts on slots in the steel band to tighten the clamp. Some genius used these around a rubber covers to keep the leafs aligned. Apparently it worked.
Modern versions of these hose clamps have a band, holder and worm screw with a 5/16" hex drive. I buy them at Lowes, all stainless steel. I use them for a lot more than just hoses. For instance, my coil is secured to my engine bay with them.