Three-ring binders vary in style according to the size and nature of the ring, the type of cover and the presence of internal or external pockets. Some binders are also available in different colors or with special features, such as zipper enclosures, additional pockets or built-in tools like calculators.
Most three-ring binders come with an O-ring style, also known as a round ring, which snaps open at the center. The other common ring style is the D-ring, which features one round edge and one flat edge. This allows the papers to sit flat against the spine of the binder rather than pushing outward. Some binders also use the O-ring style but place the rings on the back cover rather than the spine, adding additional viewing space when open. These binders include varying sizes, typically ranging from 1/2 inch to 3 inches in diameter, with the larger sizes accommodating more sheets of paper, as well as papers with heavier weights.
Some three-ring binders also include clear covers on the front and back that allow users to insert custom sheets, such as for naming the contents. These binders may also include a similar sheet on the outside of the spine for labeling purposes. It is also common for the binders to include pockets on the inside covers to store extra papers or dividers. Most binders feature open edges, though some thin binders include a portfolio cover and some larger binders offer a zipper around the edges.