Since you are buying rod, the local home improvement store if they have 12mm rod might not be the best source...so, considering you are buying a steel rod you would want a higher carbon rod in what grade steel and what hardness?
Too hard it is going to dull your dies threading it or is going to be brittle and break easier. Too soft has similar issues with deformation or stripping and not holding up...
Do you need just a general purpose and inexpensive steel or should you buy something based on the blend?
Thanks! David