Tin snips are a tool used to cut thin sheet metal, as well as other materials such as chicken wire and other mesh wire (e.g. screening), leather, and asphalt roof shingles. Tin snips work and are used in the same way as ordinary scissors, but can handle thicker and harder material. They come in three different types: straight cutting, left cutting, and right cutting, which are usually color-coded yellow, red, and green, respectively.
A similar tool known as aviation snips will cut sheet metal with less effort and can handle heavier gauges.