The BX084BR-N52 is coated with a durable layer of black rubber, very much like tire rubber. The 1" x 1/2" x 1/4" dimensions are the finished dimensions of the rubber coating, which protects the magnet from impact damage and corrosion.
These blocks can be slammed together many times without damage, overcoming one of the greatest weaknesses of neodymium magnets - fragility. The rubber coating is very water resistant, but not recommended for underwater use, as the rubber seal is not guaranteed waterproof. The rubber also helps to limit slipping on smooth surfaces like we describe in our Leverage & Friction
An all-around fantastic magnet with incredible strength. It is Grade N52 Neodymium, after all!