Monel R-405 (UNS N04405) is a free machining grade of Alloy 400. Its higher sulfur content improves machinability. It has essentially the same corrosion resistance and physical properties as Alloy 400, but with a slightly different range of mechanical properties. Monel R405 is mainly used as raw material for automatic screw machines and is generally not recommended for other applications.

MONELR-405 was developed to have good machinability and is recommended for automatic screw machines. Nickel-copper sulfide, produced by the sulfur in its composition, acts as a chip breaker.