Brass brushes are non-sparking and softer than steel. They will not scratch soft metals like gold, copper, brass. Ideal for cleaning and surface-finishing items made from gold, bronze, copper or brass Use a brass brush to create a soft, satin or matte finish Very effective on flat surfaces and in hard-to-reach areas like slots (Brass wire is non-sparking and softer than steel) Very effective on flat surfaces and in hard-to-reach areas like slots BIT DIAMETER INCH: 1/2" BIT DIAMETER MM: 12.7 mm