The Tudor Collection \'0\' Numeral Smooth Black Iron is ideal for rustic properties and is to be screw fixed. Each numeral measures at 76mm (3\") and comes complete with fixing screws. Smooth Black Iron House Number The smooth black iron finish does not have deep surface indentations like many other black finishes - this gives it a more modern feel. It is made from malleable cast iron, treated with a zinc phosphating process and then powder coated to provide a durable finish.