Read from the World of Warcraft client build files.
How Galactic Gladiator's Silk Hat Compares
Who It Suits
Cloth is the armor type Mage, Priest and Warlock wear. With Intellect, Galactic Gladiator's Silk Hat suits Discipline, Holy and Shadow Priest; Arcane, Fire and Frost Mage; Affliction, Demonology and Destruction Warlock.
Transmog Sets
Galactic Gladiator's Silk Hat is part of the transmog set Galactic Gladiator's Silk Armor (Mage only), which the Appearances collection lists in 3 versions. The other 16 pieces:
Items Numbered Next to Galactic Gladiator's Silk Hat
Blizzard numbers items as they are created, so the named items next to ID 255363 (255358 to 255368) were usually added in the same batch as Galactic Gladiator's Silk Hat: the same quest line, zone, vendor or reward set.