Top valve is a Thermostatic mixing valve that maintains a constant water temperature automatically, regardless of incoming hot & cold water pressure & temperature. Set valve to desired temperature & no need to adjust further Bottom valve is an integral volume control and on/off Anti-scald protection Lower cost alternative; no need for separate volume control, and easier installation Thermostatic & volume control cartridges are ceramic 1/2'' NPT female ports 12 GPM flow @ 60 PSI Can be used for handheld application Extension kit available for deep wall installations, see J-THVC12-EXT Ideal for tub & shower with twin ell (provided) & diverter tub spout (sold separately) Works well with low water pressure