The machine screw, a term that has confused most people at one time or other as it looks like a bolt and can be used with a nut as well. The term seems to have arisen as the term screw seemed originally to refer to all small screws and bolts. Strangely as the machine screws got bigger the term stayed the same. The development of metal box construction made the machine screw far more in demand. It is the ideal construction item when the fixing can be completed from one side of the work only. In this case a hole is drilled into the base of the unit and the hole is tapped with the screw thread of the same size as the machine screw. The top section has the equivalent hole but slightly larger drilled through the section, when the 2 pieces are offered together they can be combined by pushing the screw through the top section and screwing it into the tapped hole below. The finished joint can be tightened strongly and works extremely well.
The machine screws can be purchased from a good supplier in various sizes and lengths. The strength of the joint is generally greater than that achieved by the self-tapping screw system and they are used in places where a good strong joint with a good finish is required. Stainless steel is often used making them a strong fixing but also one that can be used on enclosures where a good finish is required. They can also be extracted and re tightened easily with the use of a screw driver to give access to the enclosure but in contrast they are often used as a security fixing. In this case the screw is fitted with a security screw system which requires a special screwdriver only available from special sources controlled by the manufacturer. These are often used to keep people from accessing specialist or dangerous equipment where nuisance or malicious damage can be carried out or where people can gain access to dangerous electrical or mechanical equipment.
It does seem that the system has even more applications as the finished joint is so good and it could replace both self-tapping screw systems and certain nut and bolt systems to give a better and safer finished fixing. The machine screws could certainly be used more and the extra work required is very small for the rewards available and are well worth considering.