não estou muito certa, mas fica-me como uma sugestão

This is a tough one! My first impression was in the sense of "a 1-off work", for example, meaning, unique, 1-only...but 5-off? I Googled and found that this is a very common expression in the context of milling and grinding, lathes, etc. In some contexts it could mean, a machine only handles one piece at a time, while others can do 2 or 5. Some machines in the textile industry are 12 off or 16 off, apparently meaning the number of spindles of thread/filament they can handle. In your case, however, the text is about parts and tools, so I conclude that "off" is a standard expression in lists to mean "peça" or "ítem". I wish I could be more certain, but just could not confirm any more than this. HTH.