Hi,

I'm new to working with bikes and I need to sight a RD hanger. I think I understand the process. Go to the hardware store and get a 10mm fine pitch bolt that is as long as I can find and a square. take off the RD and thread the bolt into the hanger. but I'm kind of confused as to where to put the square. :s

This is exactly what my bike looks like:
See how the drop out is all slanted and it's rounded? kind of throwing me off. I'm sure it's simple so if someone could point me in the right direction.