they are impervious to chemical solutions normally used in a clinical setting preventing clouding and spidering, with 1/8 in NPTF connection.our flowmeters use black glass flow indicator ballstheir exceptional sphericity and uniform weight contribute to a more accurate flowmeter than those using plastic floatshighly accurate needle valves insure precise flow-settings the first time every timethe flow control knob is on the front of the flowmeter in clear sight of the operator unlike side mount knobs which are susceptible to damage during installation of additional equipmentour black glass float makes the flow setting easy to read1/8 in nptf.