How to change a fuel pump 91 chevy c1500 5.7?

hi im replacing the fuel pump on my truck, i know how to do it i was just wondering if anyone knew the size of the nut thats on the bolt that attaches the tank straps to the frame? thanks. and also if anyone knows any other ways to get to both of the nuts seeing as how the access hole on te frame is tiny. thanks again!How to change a fuel pump 91 chevy c1500 5.7?long extentions and a 15 mm socketHow to change a fuel pump 91 chevy c1500 5.7?15 mm