A curtain ring is a small clip designed to hold a curtain

Curtain

A curtain is a piece of cloth intended to block or obscure light, or drafts, or water in the case of a shower curtain. Curtains hung over a doorway are known as portières...

 in place. As their principal purpose is to hold up curtains of all types, examples of their use can be found on shower curtains and other types of curtains.

Usage

The Romans used curtains hanging from poles with a few rings. Pliny's natural history reports that the hard kernels of the cucus tree were turned to make the rings.

Lewis and Clark

Lewis and Clark Expedition

The Lewis and Clark Expedition, or ″Corps of Discovery Expedition" was the first transcontinental expedition to the Pacific Coast by the United States. Commissioned by President Thomas Jefferson and led by two Virginia-born veterans of Indian wars in the Ohio Valley, Meriwether Lewis and William...

 took three gross

Gross (unit)

A gross is equal to a dozen dozen, i.e. 12 × 12 = 144.It can be used in duodecimal counting. The use of gross likely originated from the fact that 144 can be counted on the fingers using the fingertips and first two joints of each finger when marked by the thumb of one hand. The other hand...

 of curtain rings with them on their famous expedition to the Pacific coast in 1804, expecting to give them as presents to the natives

Indigenous peoples of the Americas

The indigenous peoples of the Americas are the pre-Columbian inhabitants of North and South America, their descendants and other ethnic groups who are identified with those peoples. Indigenous peoples are known in Canada as Aboriginal peoples, and in the United States as Native Americans...

 of the North American interior.

In the 19th century, Mr Rees designed a curtain ring which would not catch upon the curtain rail and so would go smoothly around curves and corners.

Such rings may be used as improvisations in other ways. For example, they may be used as a wedding ring

Wedding ring

A wedding ring or wedding band is a metal ring indicating the wearer is married. Depending on the local culture, it is worn on the base of the right or the left ring finger. The custom of wearing such a ring has spread widely beyond its origin in Europe...

 to solemnise a marriage ceremony; or as a ligature

Ligature

Ligature may refer to:* Ligature * Ligature , a characteristic notation style of the Medieval and Renaissance periods of music history* Ligature , a device used to attach a reed to the mouthpiece of a woodwind instrument...

 to prevent nocturnal enuresis. Other uses include attaching a hammer to your pants and your sneakers to your sleeping bag while camping.

The 1987 film Planes, Trains and Automobiles has a character played by John Candy

John Candy

John Franklin Candy was a Canadian actor and comedian. He rose to fame as a member of the Toronto branch of The Second City and its related Second City Television series, and through his appearances in comedy films such as Stripes, Splash, Cool Runnings, The Great Outdoors, Spaceballs, and Uncle...

who is a curtain ring salesman. His ability to sell the rings for their alternate uses is central to the plot of the movie.