When you are taking the fittings off or tightening them on make sure you use two wrenches, one to hold the fitting in the filter and one to turn the line fitting nut. I just changed my 7.5 filter and I needed a 3/4 inch, a 5/8 inch for the line from the fuel pump, a 9/16 and a 7/16 for the line from the filter to the engine. And a 1/2 inch for the filter mount nut on the stud in the centre of the filter. And you will have fuel down your sleeve if you are laying under the coach, also use a small drip pan. For a small item I am not sure why they had to design it with 5 different size wrenches to change it.
Happy changing, Bob