Use a variety of wood carving into a pattern, and some will be engraved with the blessing of the text. The types of materials are more common: rosewood, Zaomu, black and ebony and so on. Among them, zaomu the role of evil spirits in Taoism, so it is used more. (Although the walnut is also evil spirits, but the wood is relatively soft, it is rarely used as a key ring.)
As for the type of the pattern, it is very much, common is: Buddha statue, 12 zodiac and various animal statues and so on countless.