A spring tension rod is a certain type of rod that is used to create tension between a rod and the wall to which it is installed. It is comprised of two pieces that can be placed inside of one another and a coil spring which is placed inside the rod. When the two pieces get pressed against each other, tension is created and maintained by installing a screw.
Spring tension rods are used for certain types of fixtures that need to be placed in tight spots. Spring tension rods are commonly found as parts of a shower curtain, or in the installation of certain types of window curtains. Generally, they are used when the material they need to support is light. Heavier objects, when draped over a spring tension rod, can overpower the tension and cause the rod to fall.
Often spring tension rods are used to hold up a curtain without doing damage to the walls. Since a curtain is lightweight, the simple tension provided by the coil inside of the rod is enough to keep it up. Sometimes spring tension coils are used inside of other types of rods, such as those found within closets. Because they are adjustable, these rods can fit in different types of rooms or areas.