I don't know where you are, but in the UK there are generally two sizes of outside hose tap union in common use.
One is 0.5 inch BSP male and the other is 0.75 inch BSP male. If you have a 0.5 inch BSP male hose union tap and your hose has a 0.75 inch BSP female connection, just get a reducing bush (0.5 inch BSP female by 0.75 inc BSP male).
Note: All these BSP threads referred to are parallel, not tapered, so you generally need fittings with sealing washers.
Don't know the thread size but most hardware stores sell an adapter to go to 3/4 inch pipe thread which is the easiest if you are trying to connect to something else.
The Machinery's Handbook lists ANSI/ASME standard hose coupling sizes from 1/2" to 4". The size for a garden hose should be 1 1/16” OD 11.5 threads per inch. Any tap or die would have to be specially made. We could machine this in our CNC lathe, but you can buy adaptors to ½, and ¾ pipe at a good hardware store for less.
