Acorn Cap Nuts

Acorn cap nuts are hex nuts with a dome top that resembles an acorn nut or crown. Consequently, acorn cap nuts are also known as:

acorn nuts, cap nuts, crown nuts, dome nuts, hex cap nuts.

Used alone or as a cap for a hex or jam nut, acorn cap 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 are otherwise the same.

Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine). Since these acorn cap nuts have a closed end, the fastener's projecting threads must be short enough to allow the nut to be fully tightened yet long enough to allow sufficient thread engagement with the nut especially when used alone.

Acorn cap nut size refers to its nominal thread diameter. Typically, sizes range from about #6 to 3/4". Sizes less than 1/4" are listed as a number size (the larger the number the larger the size) while sizes that are 1/4" and larger are specified in inches, usually fractional rather than decimal.

Nut width and height vary with the size of the acorn cap nut.

Steel, brass and stainless steel are prevalent materials. Zinc plating and nickel plating are common finishes for steel and brass is often nickel plated.

Solid metal, closed end acorn cap nuts can be used to drive small sizes of hanger bolts, then removed to allow installation of a hex nut or coupling nut.

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