Old Shop Vacuum Cleaner Ridgid 12 Gallon Model WD12450. Found some of the new filters to be almost an inch shorter. To match this I took new filters and enlarged the center hole to accommodate the thicker bottom of the threaded post. The new filter will now slide past the threads but will seat properly. To fill the gap I took the old filter cap, turned it over as a spacer and screwed on the old mounting nut. Presto - The new filter fits snugly and stays in place.