JIC 37° fittings are widespread in hydraulic applications, while SAE 45° adapters are commonly brass and are usually confined to truck and plumbing markets.
Flare fittings are called by the size of tubing they connect to rather than the thread dimension.
For example, a JIC 37° in size -08 is designed to connect to 1/2" O.D. tubing, but the fitting actually measures 3/4" on the outside of the thread.
JIC and SAE thread dimensions match exactly in sizes -02, -03, -04, -05, -08, and -10, and so will often serve quite well when interchanged in low pressure applications, since only the seat angle varies by 8°
However, in sizes -06, -12, and larger, they will not interchange as the physical diameters are different.