The fittings play a role in the amount of air that is going into your tools. The hose does play some however, a large hose on a small opening acts more like a surge tank. The smallest opening in your system is going to dictate how much air can flow though a certain area. When you start running your tools the smallest opening is going to dictate how much air is going to move past any point. The rest just becomes surge tanks. If you run a 1/2 hose and only have 1/4" opening on your fittings not matter what you do, you are limiting your air flow. Most hardware store fittings are 1/4" or if you are lucky you can buy the 3/8" openings. The 3/8" fittings are the ones that I was always told to use for better performance of air tools and have found it to be true.
