The Tudor Collection Door Chain Smooth Black Iron adds an extra level of security to your front door - this finish works particularly well on wooden front doors. The chain measures at 106mm x 38mm and is sold individually, complete with fixings. Smooth Black Iron Door Chain 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.