You haven't said why "threads don't work with normal hose". That vacuum breaker has same threads as normal hose and is used to prevent syphoning water back into system, NOT as an adapter. If you still want an adapter,ask at big box for a wye adapter that alow's 2 hose conneceted to a single facuet. Also ask for a 3/4tr pipe thread to hose thread adapter.

Thanks so much for your information. I assumed there must be a simpler solution. I believe the faucet is over 100 years old and has pipe threads (although I'll have to check the size), so it would make sense to have a pipe thread to hose adapter, but what is the other adapter for?

The wye adapter simply alow's 2 hoses to connect to a single faucet. In your case I suggested it on the outside chance threads are damaged on faucet making it difficult to start hose onto them. Maybe you are right about faucet having something other than hose thread. If so the 3/4" pipe to hose adapter will do the trick,last longer and be cheaper than a vac breaker.

Definitely sounds simpler, and hopefully, the 3/4" adapter will fit my faucet. I greatly appreciate your detailed help, especially since I have very little house maintenance knowledge. Thank you!