Fox 4/40 pressure taps are getting hard to find but the 6/32 Dubro ones are available and work fine. If one is concerned about the opening being too large, (it's not) however if it is, a restrictor can be put in the system. One way to make one is to fill up a short length of 1/8" brass tube with solder. JB Weld will also work. Drill a small hole in the center. Shove it into the line connecting the pressure tap to the uniflow outlet. Easy, adjustable, and removable.