Washers

Washers come in a wide variety of designs and within those individual designs are a range of materials, dimensional variations and finishes.
Many can be used either under the head of the fastener, bolt or screw, or under the nut.
Many can be encapsulated as an assembly on a screw or bolt, or occasionally with a nut; these products are called SEMS.
Most washer sizes will be designated by the diameter (size) of the fastener with which they are to be used.
Basic Washers are employed to:
- spread the clamp load over a larger surface area
- cover an oversize or elongated hole
- reduce the friction of the rotated component
- protect the work piece surface from damage by the rotated component
- provide a locking or vibration resistant function
Specialist washers have been designed to perform particular functions in particular types of applications. These may be locking, load spreading, decorative, tension indicating, sealing, or a combination of these functions. Some of the most common are shown in the charts following.
SKETCH TITLE COMMENTS
FLAT (Black, Bright) Common general purpose basic washer, can come in various dimensional standards, quality levels, materials, hardness grades and finishes.
Could also be available square.
Often used in conjunction with a split spring washer.
SPLIT SPRING Common locking washer, will come in a variety of thicknesses and sectional ratios.
Available in various materials throughout a wide size range.
Used to resist vibration loosening.
Will damage surfaces it contacts.
BELLEVILLE WASHER
(Conical)		 For use in high vibration applications where tension must be maintained if some loosening occurs.
Can be used in stacks or series to increase the axial load or to increase the possible deflection length.
INTERNAL TOOTH
LOCK WASHER
(Shake Proof)		 Used with pan or cheese head machine screws to resist vibration.
Minimal damage to surface.
EXTERNAL TOOTH
LOCK WASHER
(Shake Proof)		 Same as above except slightly more damaging to surface.
Also available in countersunk version.
WAVE Can be available as full circle or split.
Is used in place of spring washers where surface damage is to be avoided.
Also used where some pressure is required on a free element of an assembly.
Usually confined to small diameters. Similar products are crinkle washers.
CURVED Generally confined to light applications similar to above, where only very light pressure is required.
SCREW CUP
(Cup)		 Used under a countersunk screw where a decorative or appealing finish is
required; eg. Automotive door trims.
Normally would be nickel or chrome plated, or in stainless material.
NEOPRENE
(Neo)		 A rubber type material used in roofing screw applications under washer head screws with sealing washer recess.
Designed to create a waterproof seal between the screw and sheeting material.
Can also be bonded to aluminium or stainless washers.
CYCLONE WASHERS Various styles to suit the range of roofing profiles.
Bonded with neoprene, these washers spread the load over a large area of roof sheeting, reinforcing the sheeting against lifting over the screw heads in cyclonic conditions.
STRUCTURAL A hardened steel washer used in conjunction with structural bolts in heavy construction applications. The washer reduces galling between the tightened surfaces and spreads the load.
The three external tabs identify it as a structural washer.
LOAD INDICATING
WASHER (Coronet)		 Used in the structural industry to provided evidence that the required tension has been achieved.
The raised protrusions will crush in relation to the load applied, providing a permanent witness that required tension was achieved.
   
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