Hi Thi Thai Hien,
‘Metal working (average) offsuite’ would be more specific impacts as in you are sure that it’s only steel related fabrication. Whereas ‘Offsite manufacturing/fabrication process’ would be more generic which could cover a whole range of fabrication processes (from plastic injection molding to autoclave oven etc).
If your product/item is mostly made of steel, I’d say the ‘Metal working’ option would be more relevant.
