the tip 30 being centered within the opening 45 in the air cap 26 this unique arrangement of threads in the manifold 18 insures the precise positioning of the exit end 30 of the delivery tube within the center of the hole 45 in the air cap 26 referring again to fig3 and fig5 the air cap 26 has an opening 45 which is rounded and which is precisely dimensioned to be spaced a predetermined distance away from the outer diameter of the fourth step 46 of the static mixer 14 a conical surface 47 is formed on the inside of the air cap 26 as the cap 26 is rotated the spray angle will change thereby determining the pattern which is sprayed the spacing between the opening 45 in the air cap 26 and the end 46 of the static mixer tube in conjunction with the displacement between the end 30 of the static mixer 14 and the end surface 52 of the air cap 26 controls air velocity and volume and provides the ideal spray pattern the outside diameter 48 of the conical portion 47 of the air cap 26 is slightly larger than the outer diameter of the pattern of symmetrical holes 21 so as not to block the flow of air the diameter of the opening 45 is selected to provide the optimum predetermined spacing between the tip 30 of the delivery tube 14 and the air cap.