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Parts of a Stair Stairs are more complex than they look. Each step has two parts. The horizontal part where you put your foot is called the tread. The vertical part between each tread is called the riser. The stairs are usually supported by a strong piece on each side, called a stringer. A handrail on the wall gives you something to hold for safety. The size of the tread and riser is important. They must be the right size for people to walk up and down comfortably and safely. CONVERSATION