Spiral Stairs : Stairs of this type have stair flight resembling a circle or a part of it in its shape. Here just like in Winder Stairs and Arched Stairs the treads are wedge-shaped, but all of them (except for the last one) are uniform-sized. Spiral stairs have a central vertical post constituting the backup abutment for all treads in the flight. Due to their spiral shape such staircases look very effective. Such staircases are not convenient for frequent use in view of fast climbing up on a confined area.