GolamMostafa:
The 60+ year old Safety Officer of the GEC Plant in Rugby (UK), in the year 1979, showed to the foreign customer engineers a fully straightened Crane Hook which failed at 50% active load when the Design Safety Margin of the Hook was 300%. The safety Officer suggested not to go across even underneath of an empty crane.So, what else is there to say except saying that the good design will work hopefully?
That's manufactural defects. The maker should be sued out of business along with whoever certified the parts.
We get a lot of junk cheap. After a while, what we get is most all junk.