washer, machine component that is used in conjunction with a screw fastener such as a bolt and nut and that usually serves either to keep the screw from loosening or to distribute the load from the nut or bolt head over a larger area.

When should you use washers with bolts?

Washers are used with bolt to give the nut a smooth, even surface to tighten against, better distribute pressure on softer materials and prevent pull-through. When are lock washers needed? Lock washers are needed when the fastener assembly is subject to vibration or wherever back off is considered an issue.

When can you not use a washer?

RE: When to use washer or not??

It depends on the design - geometry, materials, and forces. The washer can provide increased bearing area and higher/more consistent preload, which may be necessary. However, the design may not require extra bearing area or more consistent preload, therefore it won't need washers.