The author of "Arab Archery" refers to rings as being usually made of leather. A "thumb tip" or "thumb ring" which is called "kustubān" by the Persian and "khayta‘ah" by the Arabs, consists of a ring of leather or some other material. It is worn over the right thumb, leaving the nail and knuckle exposed, and is use for the protection of the thumb against injuries which are usually caused by the string when it is drawn and released." Possibly, most ordinary archers historically used tabs of leather, much cheaper and easier to make, but such rings are not likely to survive. Metal thumb rings of silver or bronze were thought to be too inflexible in use, and thus were less accurate.