Steel Perforated spiral staircase steps are available in all welded, standard and heavy duty kit units. They can be used interior or exterior. Most commonly requested for maximum traction capabilities for residential, commercial and industrial applications. Step consists of ¼" frame with perforated sheet material welded to frame. Perforation is a ¼" round hole with raised dimple. Great choice for snow and ice. Has a contemporary look for the right interior application.