The lack of strength

What happenes if you overestimate the power of your arms? The bolt is undertightened and burnt. Lincoln Electric Power Feed 25M was damaged due to the lack of attention.

 This is how the bolt was burnt while the welding current was going through it, because of the lack of contact between the welding current carrying bar and gun adaptor.

 As well as bar.

 And gun adaptor

 And so on ...

It happened because of the engineer who does not tighnened the fixing bolt properly. As a result the welding current went through the tightening bolt instead of the very contact.