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MACHINE SCREW, NUTS AND WASHERS
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MACHINE SCREW / BOLT NUTS
 

DOME NUT: Supplied with most machine screws / bolts are nuts, to lock the bolt in position. They are supplied in a range of types and sizes.

Dome nuts are regarded as both functional and decorative. They are often chromed as a finish or are manufactured from brass or stainless steel.

 
     

HEX NYLON LOCK NUT (left)
SELF LOCKING LOCK NUT WITH BUILT IN FRICTION RING (right):

Lock nuts are used when it is vital that the ‘nut and bolt’, does not rattle loose. Some have a nylon insert, that the machine screws thread cuts into when being tightened. The nylon provides and necessary friction required to prevent ‘loosening’ on the nut. Other lock nuts have a built-in friction ring, which serves the same purpose.

 
 
 
 
A Castle nut and Split Pin can be used to ‘lock’ a ‘nut’ in place, as shown in the diagram below. The split pin pushes through a hole in the bolt and is deformed through the castle nut, preventing it from loosening.
 
 
WASHERS FOR MACHINE SCREWS AND BOLTS
 
PLAIN WASHER: Washers for machine screws and bolts provide the surface on which the nut or head of the bolt are tightened. When tightened, the force applied to the bolt / nut is distributed evening across the area of the washer. This prevents the area around the head of the bolt and nut from being damaged.  
 
 
 
CUP WASHER: These are used in conjunction with countersunk screws (wood screws and machine screws). The machine screw head fits neatly into the cup, providing a professional finish. They are often decorative and can be seen on knockdown furniture and are often brass or chrome finished.  
     
SPRING WASHER (LOCKING WASHER) AND STAR WASHER: A spring washer (also called a helical spring) is designed to prevent a nut from loosening. The ‘spring’ exerts a force against the bolt head / nut, making it less likely that the nut and bolt will loosen.
A star washer has the same function, in that it helps to prevent nuts and bolts becoming loose, through vibration or shaking.
     
 
 
 

RUBBER FLUTED WASHER: A rubber fluted washer provides a waterproof seal for exterior work, such as felting a shed room, when roofing screws are used.

The example opposite, shows the rubber fluted washer ‘compressed’ under the force applied through the screw, creating a seal.

 
 
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