Originally Posted by rubberchicken
Royal Purple filters , at least up to 1/1/19 (and possibly later but I cannot confirm), were made by Champion Labs and are almost identical to M1 and Amsoil filters. Exceptions are the ADBV (its Purple !! ), and the media "might" be slightly different.
Almost... The M1 is NOT full synthetic media (it's a blend), and it's not wire backed either. The RP is similar to Amsoil, Fleetguard Stratapore, upper end Donaldson, even an Ultra (with a stronger, heavier can).