Deck stairs normally have 3 stringers, which are the long pieces of wood that bear the weight from the stair tread. The stringers are on both ends and a single one in the middle.

Besides transmitting the load to the both the upper and lower floors, the stringers have a stair step pattern cut into them, so that the stair tread and riser can be fastened.

Stair stringers can be fastened to the floor by using a joist hanger or metal bracket.