Male Sae O-Ring Boss-Male Bspp

For that setup, you are looking at the right style. One end is a 1/2 inch male SAE O-Ring Boss with 3/4-16 UNF threads, and the other end is a 3/4 inch male BSPP with a G 3/4-14 thread, in a straight steel fitting.

That's exactly what this one's built for. One end is 1/2" male SAE O-Ring Boss with a 3/4-16 UNF thread, and the other is 3/4" male BSPP with a G 3/4-14 thread. It goes straight between those two connection types with no extra adapters needed. Steel construction, straight profile, 32mm wrench flat to torque it down proper. At 41.4mm overall length it's a pretty compact inline solution for that exact crossover.