Acorn nuts are hex nuts with a dome top. Consequently, acorn nuts are also known as:  cap nuts, crown nuts, dome nuts, hex cap nuts.  

Used alone or as a cap for a hex or jam nut, acorn nuts serve a decorative purpose by concealing the threaded end of a fastener or acting as a cover for protruding, perhaps sharp threads.

Some types are manufactured in two pieces and pressed together, others are milled from a single piece of metal.

Aside from a possible slight difference in dimensions, both types of cap nut otherwise the same.

Size: M6-M24

Hight: as per size

Hex hight: as per size

Width across flats: as per size

Thread type: metric corse/fine right-hand thread

                    imperial thread is available upon request

                    left-hand thread is available upon request

Material: steel

Grade: 4.8/6.8/8.8/10.9/12.9

Finish: plain/black oxide/zinc plated (galvanized)/hot dip galvanized (HDG)

           other kinds of surface treatment are upon request

Technical info: DIN 1587