Hi:

I was trying to change the gasket for my shower knob. I removed the knob, removed the hex nut inside using a hex head (please see the first picture). To my surprise, there was another hex nut inside! (please see the second picture) I couldn't remove this second hex nut because the space inside the copper tube was too narrow for a hex head. I tried to pull hard or to remove the copper tube, but neither was successful. Your help will be greatly appreciated!

Use a pipe wrench to remove the "copper tube". It screws onto the fixture. Go counter clockwise to loosen. You may damage this piece but it is easily to replace. An alternative method is a thin wall socket available in the plumbing tools section of most hard ware stores.