521616A Caleffi 521 MixCal 1" Press Union.

Adjustable thermostatic mixing valve for point of distribution in  domestic water systems and radiant hydronic heating systems.
Low-lead brass body. Locking set point knob. Max. working pressure: 200 psi. Max. inlet temperature: 200 ºF. Adjustable range: 85 – 150 ºF.
Min. flow for optimum performance: 1.0 gpm. (0 gpm with recirculation. gauge scale. 30-210 F.