3 way molded heater hose for SPI systems. This junction attaches the thermstat sandwich plate, heater valve, and throttle body. These are becoming hard to find. 
 
It is very common for people to avoid replacing these junctions, but they will leave you stranded if they blow. This was used on all standard SPI engines, but the JDM MPI cars (MPI block / SPI Injection) used a slightly different hose (PCH113760).