It is pass/fail, not A,B,C,D&F grades.
“In bolt security there is failure or no failure,” Nord-Lock International A.B. global research & development director Maxime Thonnerieux told Fastener+Fixing magazine. “There is a lot of unseen engineering behind two apparently simple washers.”
“They have to allow a perfect tightening process, (…)
via “In bolt security there is failure or no failure.” – Global Fastener News – USA.