1/2 inch In-Line Probe Holder allows laboratory grade probes (except conductivity) to be inserted directly into new or existing PVC lines. This type of probe installation provides very accurate parameter measurements as water is continuously flowing across the electrodes. 1/2 in. MTP fitting screws directly into PVC T-fitting for quick and easy installation. Ball valves should be placed on both ends of the probe installation to allow for easy removal of the probe during maintenance and calibration.