PRODUCT DESCRIPTION Used in applications with nuts and bolts. The flat washer provides a greater bearing surface which helps prevent a nut or bolt head from tearing through the material. Flat washers are commonly used in decks and fence building. The called out size is the inner diameter of the washer. FROM THE MANUFACTURER Used in applications with nuts and bolts. The flat washer provides a greater bearing surface which helps prevent a nut or bolt head from tearing through the material. Flat washers are commonly used in decks and fence building. The called out size is the inner diameter of the washer.