You may never think about flat washers until you need them, but they are indispensible in a host of applications and available in hundreds of different shapes, sizes to suit different projects. Below are the most common types offered by Shunfeng, a professional manufacturer of metal washer .
Flat washer, also know as plain washer, is a thin, flat annulus or ring, in both zinc plated steel and stainless steel. With a larger bearing surface, it is used under a bolt or nut to distribute the load of a screwed fastening as well as protect the surface being fixed. Additionally, flat washers prevent loosening under vibration as well as avoid galvanic corrosion if you use steel bolts on an aluminum surface.

Details:
Material: steel in grade 4.8, 8.8, 10.9 and 12.9; stainless steel 304 and 316.
Finish: plain, zinc plated (clear, yellow or black).
Inside diameter: M6 to M54.
Thickness: Any custom thickness is available.
Package: plastic bags and paper carton.

Types:
Standard flat washer 
As the most common type, a standard flat washer features two flat surfaces that make it efficient to distribute fastening forces, reduce vibration, friction as well as heat generated during installation. Available in GB, USS, SAE types for all purpose low strength fastening.
Heavy duty flat washer 
Made of stronger and thicker material - 45H carbon steel, heavy duty flat washers allow for extra strength and better load distribution properties. Diverse applications include general industries, machinery, powder transmission and various heavy duty bearing uses.
Fender washer 
Wither larger outer diameter in proportion to the central hole, fender washers provide larger working areas for more efficient force distribution. They are incredibly well suited for plumbing, electrical industry and sheet metal applications such as fixing signs, panels and drywall.
Dock washer 
A dock washer refers to a washer in larger outside diameter and thickness compared with the fender washers in the same size. Normally, they are used in dock, wood construction and various heavy duty load bearing applications.