We stock here at Caleb Components, Single Coil Spring Tension Washers (with rectangular section) to DIN 127B Standard. These washers can also be known as Split Washers
Our sizes range from 3mm up to 30mm.
As they are bent into a helical shape, this enables them to exert a spring force between the fastener head & substrate.

Please click on below link to see our full range of Single Coil Washers.
https://springfasteners.co.uk/product-category/washers/single-coil-washers-din-127b/