Box Modern Retreads are made of .625 inch thick solid wood slabs with a modern nose profile that simulates a 2.25 inch slab of wood. Modern Retreads are available from 36 inches to 60 inches in length. Modern Retreads are used for remodeling an existing staircase. The staircase must have closed stringers to use box Retreads if there is an open stringer on one or both sides you will need a Modern return Retread. This product will cover dimensional lumber treads without the need to install a new riser on the staircase.