nut

What is the size of the little screw that locks the flower nut in place? I need to pick up a new one at a hardware store, or order one online.

For some reason, I did not receive the nuts for the gas tank in my kit, and I was wondering what type and size nuts I need to use to screw onto the gas tank stubs to mount it to the bike? I will be visiting the hardware store once I know this, or bring the tank to the store. I just joined this...