The numbering system. AutoZone and O’Reilly uses the Bendix numbering system for their “basic” brake pads - MKD906 for example. But go with Duralast Gold or BrakeBest Select it’s DG906 or SC906. It’s like filters using the Fram, Purolator, Champ or Wix numbering.
IIRC, FMSI does have...