Someone may have already mentioned this, but according to the rules/instructions of Nomenclature, you should always classify things that are part of larger piece (parts, broken off sections etc) as the whole object with the description telling you it is not whole.  Some cases, like lamp shades, which are typically a separate item have their own classification listing.
So in the case of the shares as they are called, they would typically be classified as a plow if just loose from the plow.  However, they could be sold separately as a replacement part, so you could add the term, "Share, plow" under Agriculture to distinguish these replacement shares from the ones that typically can on the plow.   So with the new system, you could do as you suggested and add Share (not blade) to your secondary term under plow if you wanted.  Before  you add your term however, be sure you know if what kind of a blade that you have since there are actually  shares, shins, plow points or shears, and moldboards so that you do not misidentify them. There are great diagrams available online that identify the parts of both plows and cultivators to help identify these parts.
Good Luck
Tracie


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