Brass Nuts
A nut is a type of fastener which has a threaded hole of various shapes. A nut is used in a bolt mechanism as a tool to tighten the entire assembly and to hold it in place. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts. In applications where vibration or rotation may work a nut loose, various locking mechanisms may be employed. The most common shape is hexagonal, for similar reasons as the bolt head - 6 sides give a good granularity of angles for a tool to approach from (good in tight spots), but more (and smaller) corners would be vulnerable to being rounded off.