Form E washers are flat metric fasteners governed by British Specification BS 4320. They are defined as having a normal outside diameter (OD) and normal thickness profile, historically categorised as "black" or heavy-series washers meant for structural engineering, heavy machinery, and steel fabrication.
Form E vs Form A
In terms of dimensional measurements, a Form E washer shares virtually identical dimensions with a standard Form A washer. However, they are distinct based on their material classification and finish:
Form A: Belongs to the "Bright Washer" series. It is typically made from bright mild steel with a smooth machined finish, commonly plated in Bright Zinc (BZP).
Form E: Belongs to the "Black Washer" series. It is made from heavier, un-machined mild steel and is overwhelmingly supplied in the commercial trade with a thick Hot-Dip Galvanised (HDG) or self-colour (uncoated) finish to withstand harsh outdoor weathering.
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