How to Choose Washers: Flat, Spring, Toothed and Conical Washers Explained

A flat washer spreads the bolt load over a larger area, protects the surface from the nut and bridges oversize holes. The normal series is DIN 125 form A and ISO 7089, with a hole of 10.5 mm, an outer diameter of 20 mm and a thickness of 2 mm for an M10 bolt (13, 24 and 2.5 mm for M12). ISO 7090 is the same washer with a chamfer on one edge, which sits better against the radius under a bolt head.

The large series, DIN 9021 and ISO 7093, has an outer diameter of about three times the bolt diameter (30 mm for M10, 37 mm for M12) and is used on soft materials such as aluminium, wood and plastic, and over slotted or oversize holes. The small series, DIN 433, is for screws with small heads and for tight designs.

Washers are made in hardness classes. A 140 HV washer is a soft, low-carbon steel washer for bolts up to class 6.8. A 200 HV washer suits bolts of class 8.8, and a 300 HV washer suits class 10.9. A soft washer under a high-strength bolt flattens or dishes under the preload, and the joint loses tension. Hardened washers to ASTM F436 are required for structural bolts (see our structural bolts guide).

Match the hardness to the bolt (property classes are in our hex bolts guide). Many cheap washers sold in bulk are soft and unmarked. If the joint is critical, ask for the hardness class in the quotation and have it measured on samples.

The split spring washer (DIN 127, DIN 7980 for socket head screws) is a single coil of steel that is flattened when the nut is tightened. It is widely used, but its locking effect is small. On a joint tightened to the full preload of a class 8.8 or higher bolt, the washer is flat and its spring force is a tiny fraction of the bolt preload, so it does not prevent loosening from vibration. It does help to maintain a minimal load on soft or low-strength joints and gives a visual sign of tightening.

For vibration, choose a locking nut, an adhesive thread-locker, or a wedge-locking washer pair designed for the purpose. A conical spring washer (DIN 6796) is different: it is a stiff, conical disc used under a bolt of class 8.8 to 10.9, which keeps part of the preload when the joint settles.

Toothed lock washers (DIN 6797 internal or external teeth) and serrated washers (DIN 6798) bite into both the nut and the surface. They are used in electrical earthing, on thin sheet metal and in light assemblies, where the teeth also provide a grounding path through paint. They should not be used on hardened surfaces, where the teeth cannot bite, nor on a soft surface that you need to keep undamaged.

Washers are made in carbon steel with plain, zinc-plated or hot-dip galvanized finish, and in stainless steel A2 or A4. Match the washer finish to the bolt and nut, to avoid mixed corrosion behaviour. Use stainless washers with stainless bolts (see our stainless steel guide), and in a joint between stainless and aluminium use a nylon or insulating washer to prevent galvanic corrosion.

Spring and conical washers are made from spring steel and are zinc plated or coated in a zinc flake, because plain spring steel rusts quickly. Electroplated spring steel needs a baking step against hydrogen embrittlement, so ask how the supplier controls it.

Check the inner and outer diameter and the thickness with a vernier caliper, and flatness for flat washers. For spring washers, check the free height and the end gap, and test a sample under load. Look for burrs on the edge, which can cut into a surface, and for even plating without rust spots. Pack by size and type and label the carton, because washers of different thickness are difficult to tell apart on site.

• Standard and series (small, normal or large) in the order.
• Hardness class when used with 8.8 bolts or stronger.
• Material and finish matched to the bolt and nut.
• Quantity per size, since washer sizes run into millions of pieces.

Global Fasteners Exports is a trading and export company: our washers are made by partner factories and we handle inspection, packing, documents and shipping. Because we buy in volume from those factories, prices are typically up to 30% lower than the market price.

For washers, give the standard and series, the hardness class and the finish of the bolts they sit under, so the whole fastening set matches.

Washers are packed in cartons by size and type, and a pallet holds a very large number of small pieces. Send the standard, size, hardness, material and finish, and quantity per size.

• Samples or detailed photos can be arranged before a bulk order; sample and courier costs are normally adjusted against the first order.
• Standard payment terms are 50% advance to confirm the order and the balance before dispatch.
• Documents: commercial invoice, packing list, certificate of origin and bill of lading, plus mill test certificates and inspection reports on request.
• Different products can be combined in one consolidated FCL or LCL shipment.