Are serrated washers effective
against bolt loosening?
Serrated lock washers increase the friction between the bolt head/nut and the mating surface. They do this by gripping into the mating surfaces. Serrated lock washers are installed between the bolt head/nut and the mating surface. The bolted joint is then tightened in the same way as an unsecured bolt. If the bolted joint experiences a loss of tension, the washer is no longer effective and must be replaced.
Single part serrated washers can damage painted/coated surfaces because they have a tendency to rotate with the fastener. This risks damaging the surface, cracking the paint/coating and causing corrosion.
Read the full version in the eBook "Why do bolts loosen?"
(A comparison between common bolt securing options)
Scroll down to access the ebook.