Particle or chip board shelves are very useful but typically the material is not that sturdy. You probably have over tightened a screw in one and stripped out the hole leaving a loose screw that has no bite in the wood. Or use a shelf long enough and the boards start disintegrating leaving a constant dusting of sawdust on the floor. Instead of repairing it, most folk end up just junking the whole thing, creating waste and clogging landfills. Well, it turns out there’s a very simple and cheap way to fix particle board!