Schematic part number 10 locking nut it's either eight mil or 12 mil variations on models years,use Torx only T bar to unlock
as mentioned the retaining lock screw requires a centre punch to free it up before removal of the locking screw.
park brake pad can be adjusted from the front at 3'0clock position if you have a single rear wheel unit. Note: same as front for removal of retaining lock screw.
Richard