Though most commonly depicted as cylindrical objects, rounded edges are only one of many available options for these rods. Square, hexagonal, and flat rods are commonly stocked with custom rod shapes also readily available. These qualities render titanium 45% lighter than steel of comparable strength and twice as strong as aluminum, copper or brass with only a 60% increase in volume. Resistance to acid, stress, oxygen, salt, and microbiological corrosion make titanium the logical and most effective choice for underwater applications, as well as medical implants and prosthetics as it eliminates concern for allergic reactions to the material.