A baluster is a decorative type of stair part used to fill the open area between the railing and the floor or tread. They add style, safety, stability and support to the balustrade. Coffman Stair Parts offers a wide range of in-stock species like Red Oak, White Oak, Poplar, Hard Maple, and even Primed. All balusters fall into one of the following two categories: Pin Top or Square Top. With Pin Top Balusters, you use Non-Plowed Handrail and with Square Top, you use Plowed Handrail.