Any fitting bolt will work. No significant torque with a hand auger.
I broke the wing nut on my 6" lazer after a number of years of hand drilling. Its not the torque by itself, its the constant rocking as you drill a hole (particularly when you get tired and can't make a smooth revolution without stopping each turn). That combined with the fact that the bolt/wing nut tends to come loose a little and there is some play in the system. I was lucky, it broke but stayed together. Now that I am using a clam plate on this same auger, I check the wing nut fairly frequently.