Micro Matic Secondary CO2 Regulator (60 PSI) 
A secondary CO2 regulator by Micro Matic.
The gauge goes up to 60 PSI, and the safety pressure relief goes off at 55 to 65 PSI.
It has a brass body, and aluminum bonnet.
There is a shut-off valve with a 3/8" OD barb for an outlet, and a 3/8" OD barbed inlet.