An acorn nut with a hole drilled in it can be used as the nozzle for the Hot End of a reprap-type plastic extruder. Acorn nuts are also known as domed nuts.
Acorn nuts are available in a variety of materials, such as brass, steel, stainless steel, and nylon.
For the purpose of making a hot end nozzle, brass or steel are best, since these have high thermal conductivity and are easily machined.
To transform the acorn nut into a nozzle, a small hole must be drilled in the center. It is difficult to obtain conventional drill bits in sizes of 0.5 mm diameter or smaller. Drill bits used for drilling holes in printed circuit boards as part of their manufacture are available in this size range.
One technique for drilling the hole in the end of the acorn nut is as follows: Making a nozzle at home
There are at least two separate ways that acorn nuts are constructed. Some are made by pressing a domed piece of metal into a groove on a conventional nut. Others are made by machining the nut out of a solid piece of metal (usually brass). As the picture below shows (blob of white PLA visible at edge of dome), sometimes a small gap may be present between the dome and the nut body which will allow molten PLA or ABS to leak through. Nuts made of solid metal do not have this problem.