In Splatoon gear, each clothing item can have at most three secondary subslots. These smaller slots sit alongside the item's main ability slot and hold additional passive perks.
Gear is organized into three categories: headgear, clothing, and shoes. An item's star power determines how many secondary slots are available, so newly acquired gear may begin with fewer than the maximum. As the gear gains experience, additional slots can unlock.
Secondary abilities can be assigned or changed through the game's customization systems. Players may spend ability chunks to place a desired ability into an empty slot, while unwanted abilities can be scrubbed or rerolled using services and currency.
The number three refers only to secondary subslots, not to the total number of abilities on the item. A fully developed piece has one main ability plus up to three secondary abilities. This distinction is a frequent source of confusion when players count a gear item's complete build.