Choosing Washers and Locking Washers

Choosing Washers and Locking Washers

A washer occupies one line on a drawing and is often bought as an accessory. Yet wrong choice causes loosening, surface collapse and coating damage. Knowing which problem each type solves matters more than part numbers.

Plain washers spread the load

A plain washer spreads clamp load over a larger bearing area and lowers pressure on the joint face. On aluminium, plastics or thin sheet, tightening without one lets the head sink into the material and preload decays within minutes. A washer also bridges oversize or punched holes.

Hardness grades matter. Standard washers at about 200 HV suit joints up to grade 8.8; grade 10.9 and above need hardened 300 HV washers, otherwise the washer collapses first and preload is lost. Hardened washers also need a de-embrittlement bake after plating.

Spring washers: narrow limits

A spring washer relies on the split offset, its edges and elastic rebound. It is cheap and forgiving, but under transverse vibration the edges bite into the face and the elastic force decays. German practice no longer lists DIN 127 as a locking method, and automotive users judge by vibration tests such as DIN 25201. The point is not that spring washers are useless, but that they belong to short bolts, low preload and softer joints; high-strength and vibration-critical joints need wedge-locking washers, thread adhesive or nylon-insert nuts.

Toothed, conical and wedge types

External and internal tooth washers bite into the surface and combine locking with electrical continuity, which suits earthing and thin panels, at the cost of coating damage. Conical spring washers give long elastic travel in little space for thermal cycling and soft materials. Wedge-locking pairs give the strongest resistance but must be matched and checked before reuse.

Selection order

Identify the dominant failure mode first, then check space, assembly method, hardness, material and coating against the bolt grade.

Conclusion

Washers belong to the joint system. Zhuhai Jiali Hardware (FASTKING) supplies plain, spring, toothed and conical washers to matched hardness and coating. See the screw calculator directory or contact us.