either this one or the other one

[navi tasan]

Are you sure you have given me the right code?
1) -Either code A or code B will work. I don't know which one is the right one. Try them.
2) --Code A or code B will work. I don't know which one is the right on Try them.

Do #1 and #2 work in this context?

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Is there any day of the week when he's free?
3) He should be free one day towards the end of the week. Either Thursday or Friday will be fine. I don't know which. Just ask him.
4) He should be free one day towards the end of the week. Thursday or Friday will be fine. I don't know which. Just ask him.

Do #3 and #4 work in this context?

The idea in all cases is that both options aren't good. Only one option in each case works and is good. The speaker doesn't know which one. The sentences are like 'We know John or Harry stole the ring. We don't know which yet."

Generally when one says 'Either A or B will work', the meaning is that you can take your pick. Either one will work.

 

[jutfrank]

either A or B

This is talking about only one of the two options.

both A and B

This is talking about two of the two options.

 

[Tarheel]

I'm not sure which is is the right one. Try one. If that doesn't work try the other one.

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He's free on either Thursday or Friday. I'm not sure which. You'll have to ask him.

I wouldn't use 1) because it might be confused with "either one works".