 When the ends differ in size, it is known as a reducing (or reducer) elbow.A 90º elbow, also known as a "90 bend", "90 ell" or "quarter bend", attaches readily to plastic, copper, cast iron, steel, and lead, and is attached to rubber with stainless-steel worm drive clamps.Other available materials include silicone, rubber compounds, galvanized steel, and nylon.