This is OPTIMUS 600A Electrode Holder - For Professional Welders
This is the handle that a welder holds when doing arc welding / stick welding (MMA welding).
What is it use for?
It's the holder for welding rod / electrode.
You know when welder wants to weld iron gate, tank, pipeline - he has welding machine, and he puts a silver stick called electrode (e.g. 6013, 7018) inside this blue holder. This blue holder carries the heavy current from the welding machine to the electrode to create the spark that melts iron.