That's a Wedgewood Tech ph probe holder/ conductivity probe holder. It's 1" triclamp. I have two of them, on the HLT and the MLT loop. I'm using a Hach ph transmitter instead of the wedgewood since the Hach does auto temp correction. The conductivity probes use the stock transmitter that puts out a conductivity and a temperature output.
I use Chugger pumps with stainlrss heads.