Plumbing - Thermostatic Mixing Valve (Hidden)
http://www.supplyhouse.com/Taco-5121-F2-Series-5121-F2-Lead-Free-Mixing-Valve-No-Fittings $56.04 without fittings
ASSE 1070 and NSF 61 certified.
Will need adapters to 1/2" PEX as it is 9/16 - 24 UNEF use for 3/8” flexible hose connection.
Hot Supply Temperature: 120-180 deg F.
Min. Temperature Differential Between Hot Supply and Mixed: 10 deg F
Outlet Temperature Range: 95-118 deg F
Accuracy of Outlet Temperature: +/-3 deg F
4.5" tall. Can be mounted up-side-down (and it's typical to have knob on bottom).
Buy the version without fittings because even the adapters are 3/8" compression thread fittings.
Need to buy three of the following adapters to get to 1/2" MNPT...
Then fit an adapter from 1/2" FNPT to 1/2" PEX...