Zhuocheng M4 - M10 DIN 986 Stainless Steel 304 Nylon Insert Self Locking Nut Hex Dome Nut

The end story is, wherever bolts, nuts and rods are exposed, cap nuts are used to protect threaded fasteners, from construction and machinery to cabinets. Usually, cap nuts are dome nuts, or more specifically, domed hex nuts. They're sometimes called acorn nuts, which are in fact a type of nut cap. An acorn nut, also referred to as crown hex nut, blind nut, cap nut, domed cap nut, or dome nut (UK), is a nut that has a domed end on one side. Also known as a cap nut, an acorn nut is a type of nut that's characterized by a dome head. While other nuts are open on the top and bottom, acorn nuts are closed on the top. The top of an acorn nut resembles a dome, thereby restricting their usage to the very end of a bolt. 

How to install cap nuts. A push-fit cap nut is positioned over the stud and pressed down either by hand or with a light tap of a rubber mallet. If the cap nut is threaded, they simply screw onto the bolt and tighten with a wrench or allen key.