A process variable monitoring system for measuring a process variable indicative of a flow rate of a process fluid in a process pipe, the system comprising: a process variable transmitter; a pressure sensor in the process variable transmitter; an averaging pitot tube primary element having a neck section, a sensor section, and a transition between the neck section and the sensor section, the APT primary element extending into the process pipe and coupling process pressures of the process fluid to the pressure sensor such that the pressure sensor provides as an output pressure measurement indicative of the flow rate of process fluid in the process pipe, wherein a distal region of the sensor section includes one or more slots and is sized such that for larger diameter process pipes the one or more slots span a smaller percentage of the pipe diameter than for smaller diameter pipes; a mounting assembly configured to mount the APT primary element to the process pipe and provide a process seal such that a length of the APT primary element extending into the process pipe is adjustable for different sized process pipes and the mounting assembly comprising: a mounting weld coupling welded to the process pipe over an opening in the process pipe and having the APT primary element extending therethrough into the process pipe; an extension pipe nipple having threads on first and second ends and the APT primary element extending therethrough such that the transition between the neck section and the sensor section of the APT primary element is positioned inside the extension pipe nipple, wherein a first end of the extension pipe nipple is threaded into the mounting weld coupling; and a union component having first and second ends and having the neck section of the APT primary element extending therethrough, wherein the second end of the extension pipe nipple is threaded into the first end of the union component; a ferrule surrounding the neck section of the APT primary element; and a cap which threads onto the second end of the union component to compress the ferrule within the union and to create a ferrule process seal around the neck section of the APT primary element. a process variable transmitter; a pressure sensor in the process variable transmitter; an averaging pitot tube primary element having a neck section, a sensor section, and a transition between the neck section and the sensor section, the APT primary element extending into the process pipe and coupling process pressures of the process fluid to the pressure sensor such that the pressure sensor provides as an output pressure measurement indicative of the flow rate of process fluid in the process pipe, wherein a distal region of the sensor section includes one or more slots and is sized such that for larger diameter process pipes the one or more slots span a smaller percentage of the pipe diameter than for smaller diameter pipes; a mounting assembly configured to mount the APT primary element to the process pipe and provide a process seal such that a length of the APT primary element extending into the process pipe is adjustable for different sized process pipes and the mounting assembly comprising: a mounting weld coupling welded to the process pipe over an opening in the process pipe and having the APT primary element extending therethrough into the process pipe; an extension pipe nipple having threads on first and second ends and the APT primary element extending therethrough such that the transition between the neck section and the sensor section of the APT primary element is positioned inside the extension pipe nipple, wherein a first end of the extension pipe nipple is threaded into the mounting weld coupling; and a union component having first and second ends and having the neck section of the APT primary element extending therethrough, wherein the second end of the extension pipe nipple is threaded into the first end of the union component; a ferrule surrounding the neck section of the APT primary element; and a cap which threads onto the second end of the union component to compress the ferrule within the union and to create a ferrule process seal around the neck section of the APT primary element.