The archer’s right thumb ring, or archer’s thumbstall, was designed to help improve target accuracy and greater traveling distance of an arrow released from a bow. This type of ring was used as far back as the Han Dynasty (206 B.C. – 220 B.C.) in China, from where it was adopted by nomadic mongols who introduced the concept to Persia, Turkey, and India.
It originated having a more functional purpose, but developed into status indicators. Possession and display of these ring identified a person as high rank or royalty. Rings began to become so increasingly elaborate and decorative. It is suspected that such highly ornamented rings were only meant for display, since the uneven surface would disturb the intended proper function. When not worn or in use, they were tied to a sash and worn at the waist.
This kind of ring is an ancient example of form following function in jewlery.The extended shape of the ring identifies it.
This site shows how an archer would wear and use the thumb ring. http://www.primitiveways.com/archer’s_thumb_ring.html
Untrachti, Oppi. Traditional Jewelry of India. New York: Harry N. Abrams Inc., 1997. Print. p. 267-269.
Some of the images were sourced from here: http://anthromuseum.missouri.edu/online/thumbring/thumbring.shtml