A visit to Nord-Lock Switzerland gave me a good insight on how to choose the right size and type of washers to secure the battery terminals.
Conclusion: Before relying on a washer, try out different types and look for the “click” when loosening the bolt – otherwise you might not get what you expect.
Hex High Tensile Bolt SAE J429 Grade8, Material: 40Cr, From Ningbo S&D Metalwork Co.,Ltd, www.sendingmetalwork.com