Cap nuts cover protruding fastener threads to protect them or to prevent them from gouging or scraping nearby objects. Cap nuts are sometimes confused with acorn nuts which are also domed but come up to a point. Unless the customer specifies a specific type, either can be supplied, but it's usually a cap nut. 

Hardware Everywhere’s experts are nuts about nuts. Call them at 1-800-432-8979 or contact them online all your fastener needs.