Round flat washer

Round flat washer from Thomas Potter Ltd

A plain washer, or flat washer is a flat ring used to spread the load of a screwed fastening.

A plain washer may be used when the hole is a larger diameter than the fixing nut.

Metric washers are classified according to BS4320 and their dimensions vary according to different categories known as "Forms"

The forms go from A to D for Bright Metal and denote outside diameter and thickness. They can be summarised as -

  • Form A = Normal Diameter, Normal Thickness.
  • Form B = Normal Diameter, Light Thickness.
  • Form C = Large Diameter, Normal Thickness.
  • Form D = Large Diameter, Light Thickness.
  • Forms E to G relate to Black Metal Washers.

Dimensions are shown for reference below.

Washers are available from stock in self colour mild steel, zinc plated mild steel, stainless steel, brass and nylon.  Other materials available to special order.

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