Increased Diameter Washers

An increased diameter washer is a fastener in the form of a flat washer with increased thickness and outer diameter, or increased bearing area. The outer diameter is approximately 3 times larger than the inner diameter. It is used when mounting parts and structures on thin sheet material — metal, wood, profiled sheet — to reduce the pressure of a bolt or nut on the surface. This protects the sheet from deformation or being punched through. This fastener is also needed when there is a non-standard hole, to cover it. The washer is not used on its own, only together with other fasteners.

The original name for this element was body washer (increased diameter), since it was developed for the automotive industry, in particular for joining body panels and other flat materials. This was a way to avoid their deformation. Today, welding has taken over the fastening function for such joints, and washers have come to be used in other fields: instrument making, mechanical engineering, construction, furniture manufacturing, and other industries.

Manufacturing standards

The increased diameter flat washer is manufactured to DIN 9021, with GOST 6958-78 as the domestic equivalent and ISO 7093 as the international equivalent. Under GOST, the manufacturing product grades are A and C for all sizes, where A is high precision and C is coarse. The exception is diameters of 42 mm and 48 mm, which are produced in grade C only. DIN 9021 increased diameter washer sizes range from M2 to M36 by thread diameter, unlike GOST, where the range is 1–48 mm. Up to a diameter of 17 mm, washers are grade A; for diameters over 17 mm, grade C. The thickness under GOST can be changed on individual customer request, and by agreement washers with inner diameters of 12.5, 14.5 and 16.5 mm are also produced.

Materials

General technical requirements are set out in GOST 18123-82. The main materials used to manufacture increased diameter washers:

• alloy steels grade 11;
• corrosion-resistant (stainless) steels grade 21-22;
• aluminium alloys grade 31, 35 and 37;
• brass grade 32, 33;
• bronze grade 34;
• copper grade 38.

Quality parameters

The surface must be smooth, free of cracks, burrs, rust and other damage. Minor dents, flattened burrs on the cylindrical surface, and defects permitted by the requirements for the base material are allowed. Under GOST 6958-78, to extend service life, washers can be coated with protective finishes: nickel, copper, tin, and these fasteners are also zinc-plated. Thermal diffusion coating is also possible. Washers with a protective coating are used outdoors, in conditions of high humidity or temperature.

The appearance of the products is checked visually. The surface is assessed by comparison with reference samples, and dimensions are checked with measuring instruments or templates. Dimensions and the perpendicularity of surfaces are also verified.

About FLOK

FLOK supplies fasteners and hardware from stock and made to order.

How to order and buy

The site catalogue lets you filter products by several categories and parameters to quickly find the items you need. An online fastener and hardware weight calculator is also available for calculating your order yourself: you can enter your own data to decide more quickly on the quantity of products for your project.

To place an order, select products in the catalogue and add them to the cart. Clicking the “Send request” button opens a form where you need to provide a contact person and a way to reach you. A sales manager will contact you and advise on your order. You can also call the toll-free number or request a callback on the site.