The nutserts that I have are for the sides of the rack. I believe the center strips used a different insert. I am not sure what the thread size is for the rails. I believe the inserts were a rubber coated item. Take one of the screws to the local parts store or hardware store, and check the threads. Look carefully at the inserts, and try fastenermart.com for the ones that match. They usually sell them in packs of 50.