Hi, Randy. I'm glad that I read your other post. If you putty the spaces between the boards, you will have problems. Hree's why. The wodd wants to expand and contract across it's width. It expands and contracts in length also but by a much lower percentage. The expansion and contraction are caused by changes in humidity and, unless you control the humidity to a very tight range, this will happen. If you seal up the house in the winter and leave the doors and windows open in the summer, it will happen more.
Okay, you don't like the cracks so you put a hard putty in them. The wood will still expand but now it has no place to go. Since it still expands, it will crush the fibers in the wood next to the putty. Guess what, when it contracts again, the cracks will be back. It may take a couple of years/cycles for this to show up, but it will happen.
Don't putty the spaces between your strips of hardwood. The strips are made with a tongue and groove joint and only nailed on one side to allow this natural process to happen.
For what it's worth, I use Minwax Wood Filler (2 part) but I don't like that way that any of the fillers except stain. The is supposed to be a better filler available but I have not tried it yet since the only store that carries it just opened in our area.