I made this nutcracker nut shaped. Probably not the optimal shape for it. But it does work. I've included a longer handle that I've not yet tried out. The short one isn't too comfortable after a while. I found that I couldn't use normal hex nuts for this. They would twist and break the print. That's what's happening to the nut cracker that isn't black. The square nuts seemed to have enough holding power to work indefinitely. The damage to the bottom of the nut cracker is because I only used 3 walls for testing it. I added the rounded feature to the back to catch the nuts as they cracked. The black walnuts tend to be enthusiastic when they break. 

This is sized for a 3/8" nut and bolt.