Bicycle clips, also called trouser clips, are small C-shaped pieces of thin metal worn around the ankle when cycling

Cycling

Cycling, also called bicycling or biking, is the use of bicycles for transport, recreation, or for sport. Persons engaged in cycling are cyclists or bicyclists...

 in trousers

Trousers

Trousers are an item of clothing worn on the lower part of the body from the waist to the ankles, covering both legs separately...

. They are designed to prevent the bottom of the trousers from becoming caught in the chain

Bicycle chain

A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics. Nickel also confers a measure of...

 or crank mechanism

Crank (mechanism)

A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...

, and from being covered in oil and dirt. Additionally, they may have fluorescent (usually yellow) and reflective materials attached which make the cyclist more visible. While popular in the past, they have been largely superseded by more comfortable fabric bands, which are also more securely fastened to the leg and often larger, providing a greater visibility benefit.