(NR) Appears on a cast farm wrench (Moline Drill *), and on small cast coal shovels.
One of the shovels also says "N. M. C. Co, Chicago"
Identifying the latter might identify the former, given they start with the same letter..
The only thing I can find for NMC is an index entry for "door fastenings"
So far, it looks like a casters/foundry mark...
(-M.C - Malleable Casting???)
*Wrenching News;York Auction #273