Doesn't make much sense that you can repair it completely with an iron bar but do nothing at all with a nugget. Iron nuggets aren't useful for much more than small scale trades at the moment.
It's not economic at all to try to repair a plow before it's impossible to use it anymore, as it never needs more than one bar to be completely fixed. Letting a nugget repair about 10% would give more flexibility.
Of course this would be applied to all the repairable metal things if that's the case with other items as well.
My question was aimed more at the devs, though I'll explain it a bit better.
Currently we can use "bar on any common metal" or "string" to create/repair some objects, instead of specific objects such as "bar of cast iron" or "yarn". All these objects have the same "value"; one bar of iron or one bar of bronze will satisfy the game. Those are in the same category so it makes sense.
If you threw nuggets into the mix, then that would obviously not work the same way. That's why I wonder if the games item system can support repairing with nuggets alongside bars without rewriting stuff, or if it's a relatively quick tweak. Should it be the former it's probably way too minor a thing, I'm not advocating making this their focus or something

Yes, if this is the case for all metal objects, it may find a better home in C&I - I'll petition the demigods :p