Hammers thrown by Hammer Mario or Hammer Luigi can defeat almost everything, including Bowser, but as with other power-ups, one hit from an enemy causes them to lose their power. They also gain a fireball-proof shell when ducking (like Buzzy Beetles, which they resemble), but cannot slide down hills. Super Mario Advance 4: Super Mario Bros. 3 adds a new utility to this suit: its hammers can break Gray Brick Blocks.
In the original Super Mario Bros. 3, retrieving a Hammer Suit will make Mario and Luigi's skin turn a darker, yellowish tone which resembles the appearance of Hammer Bros in this game, while no other power-ups in the game do so. On the map screen, in official artwork, and in remakes, Mario and Luigi's skin colors stay the same when they wear the suit.
The Hammer Suit (as well as Hammer Mario) is not mentioned in the original NES or All-Stars versions' instruction booklets. The Virtual Console re-release's Operations Guide, which is based on them, also has no reference to it. In the original game, it is something of a "secret" powerup, as it only shows up in hidden areas and randomly from Toad Houses, though in later versions, it is made to consistently appear in certain Toad Houses.