Stair nosing refers to the protective edge that is installed on the front edge of a stair tread. It provides a finished look to the staircase and helps prevent wear and tear on the edge of the steps. Oak stair nosing is a popular choice due to its durability and aesthetic appeal. The stair nosing has a straight, 90-degree angle at the edge, creating a sharp and clean look. An overlapping nosing extends over the stair tread, covering the edge and providing added protection. The measurement “4 1/2” refers to the width of the overlapping portion of the nosing.