Every spiral stair manufactured by Stairways, Inc. requires a center column to which the treads are attached to form the spiral stair. Metal stairs use a column that is hollow and wood stairs use a solid core wood product. Unless the customer requests a specific type column, Stairways selects the proper column for the staircase. The metal column comes in varying diameters and wall thicknesses to meet specified load capacities. Wood columns come in varying diameters, again according to load requirements. The normal column height is the floor-floor height of the staircase increased by either 38" or 42" depending upon the height of the landing rails. The top of a column is topped off with a cap of appropriate material to match the stair being constructed. A base is attached to the bottom end of the column and is used to anchor the stair to the floor. The top end of the column is normally not attached and is covered with a top cap. Some installations require the column to be longer or shorter at either the top and/or bottom ends for certain custom applications. Such applications are discussed with the customer at time the stair order is place.