This No Lead Brass Union tee is for pressure tank installations where the tank has a 1" Female connection but with a larger diameter, 20-24".  For example AO Smith AOS205.

Tank connection: 1" MPT
The side ports are 1" MPT / 3/4" FPT
The top ports are 1/4" FPT (for pressure switch / pressure gauge)
The front ports are 1/2" FPT (for pressure relief valve / boiler drain)
Center End Length: 13"