Ring binders (sometimes called files in Britain) are folders

File folder

A file folder is a kind of folder that holds loose papers together for organization and protection. File folders usually consist of a sheet of heavy paper stock or other thin, but stiff, material which is folded in half, and are used to keep paper documents...

 in which punched pieces of paper

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

 may be held by means of clamps

Clamp (tool)

A clamp is a fastening device to hold or secure objects tightly together to prevent movement or separation through the application of inward pressure...

 running through the holes in the paper. These retainers are usually spring-loaded, frequently circular (some rings are D-shaped, others are actually rods), and may have additional latching systems.

Binder

Binder

The reaper-binder, or binder, was a farm implement that improved upon the reaper. The binder was invented in 1872 by Charles Withington. In addition to cutting the small-grain crop, it would also tie the stems into small bundles, or sheaves...

s come in many standard sizes with respect to both capacity and paper size

Paper size

Many paper size standards conventions have existed at different times and in different countries. Today there is one widespread international ISO standard and a localised standard used in North America . The paper sizes affect writing paper, stationery, cards, and some printed documents...

.