PVC Tee Type Flow Sensors are available in sizes 1, 11/2,2 inch.  They are meant for installation in PVC piping systems. They measure flow and produce an output signal to connect with control products

Brass Tee Type Flow Sensors are meant for metallic piping systems on inside or above grade installations

PVC Saddle Type Flow Sensors are used on 3,4 and 6 inch PVC piping systems.

ELF (Enhanced Low Flow}  Sensors are available  for ¾ and 1 inch piping systems and measure down to 0.2 gpm for  smaller and lower flow  systems