Bifold closet doors made from composition material such as MDF (medium density fiber board) are not as strong as wood therefore, the sockets that hold the pivot pins and rollers get worn out of shape and size with normal use. When this happens the problem gets progressively worse over time. This causes sticking and binding which places even more stress on the door and fittings often leading to serious damage. There are a few solutions out there that are just Band-Aids and only offer a temporary fix. By far, the absolutely best solution is to drill out the damaged sockets in the top and bottom of the door panel, glue Tech Team's 00935 flush fit solid wood plugs in the hole, then drill a 3/8" hole in the center of the plug after the glue has set. This, in effect, makes the top and bottom rails of the door good as new so that you can insert your pivot pins and rollers and have a door that works like new.