This filter is mostly for the purposes of maintaining the data. In putting the data into the database, I painfully went through the online wheel lists from various stores. I put a code such as "WP" or MEC to indicate one possible source for this wheel. The same wheels turn up in many stores, because they are all using the same data feed. They are not maintaining the data, they are merely displaying the data that comes from the distributor. Eg: you'll see the same wheels from "The Wheel Shop" in many stores.
You can use the MfgPart (Manufacturers Part Number) to find the same wheel in different stores.
From the document: Help for Wheel Lister