5/16" (M8) Stainless A2-70 G304 Spring Washers ANSI B18.21.1

About Spring Lock Washers

Spring Lock Washers (also called split spring or Grover washers) are flat washers cut once and twisted into a slight helix. Tightening flattens the helix; if the bolt starts to back off, the cut ends dig into the bolt head and the work face to resist further rotation. The most common and lowest-cost lock washer. Manufactured to DIN 127B (metric) or ASME B18.21.1 (imperial). Stainless A2-70 / A4-70, zinc plated and galvanised.

Frequently Asked Questions

Material & Coating

Stainless A2-70 G304 Austenitic stainless steel. Property class 70 designates a minimum tensile strength of 700 MPa with a 0.2 percent proof stress of 450 MPa. Lightly magnetic in cold-worked form, which does not affect corrosion performance.

Grade selection A2-70 G304 is the general-purpose stainless grade for outdoor and most chemical environments. A4-70 G316 contains 2 to 3 percent molybdenum, giving substantially better resistance to chlorides; A4-70 G316 is the preferred grade for marine, coastal and pool environments.

Important Do not pair stainless fasteners with plain or galvanised steel components in wet service. The galvanic potential difference accelerates corrosion of the less-noble metal.

Class Stainless fasteners are classified by property class: A2-35 / A2-50 / A2-70 in G304 stainless, and A4-40 / A4-70 / A4-80 (Bumax 88) in G316. The first digit indicates the alloy and the second is the minimum tensile strength in 100 MPa increments (e.g. A4-70 = 700 MPa). See the head marking chart and full strength table.

How to Order the Right Size Washer

Washer sizing Washer sizes can be confusing, so here is the quickest way to find the right one. If you already have a bolt or screw, match the bolt size: an M6 bolt takes an M6 washer, M10 takes M10, and so on. Look for the size at the start of the description (e.g. 'M6 Flat Round Washer').

If you only have a loose washer to match, measure the inside diameter and pick the next size down. The washer's inside is always slightly larger than the matching bolt so it slides on freely. For example, an inside measurement of approximately 6.50mm means you need an M6 washer; 17.25mm means you need an M16 washer.

The outside diameter is measured outside-to-outside. Thickness varies between batches - washers are not precision-made fasteners and slight variations are normal. All published measurements on this site should be used as a guide only.

Need every size? See our full washer gauge sizing chart for the complete SWG range (8g to 24g) in mm and inch.

Resources

Pricing & Delivery

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Disclaimer

Technical data Researched and compiled from numerous industry sources for the sole purpose of providing basic information. All material is advisory only and its use by anyone is entirely voluntary. Reliance on it for any purpose by anyone is at the sole risk of that person, and Bolt and Nut Australia is not responsible for any loss, claim or damages arising therefrom. In developing this information, Bolt and Nut Australia has made a determined effort to present it accurately.

Measurements Sizes are taken from supplier catalogues or hand-measured and should be used as a guide. Minor variation between batches is normal. Stock is sourced from various suppliers, so differences may exist between batches in markings, appearance or finish.

Product Photos & PDF Data Sheets Represent the product type, not exact size. PDFs are a reference guide only. Specifications may change without notice.

If you see any problems with any of our specifications or you require additional information please contact us.