I have a non-o visa but they want a letter from [us] embassey .. what exactly is this letter and what dept. @ embassey to get it?

You would do an affidavit at the american citizens section of the the embassy. Normally a affidavit to confirm your residence is done.

See: https://th.usembassy.gov/u-s-citizen-services/local-resources-of-u-s-citizens/notaries-public/

You will have to make an appointment to have done. Info: https://th.usembassy.gov/u-s-citizen-services/acsappointment/

thankyou

I was asked for such a letter by my local Kasikorn branch when my wife and wanted a joint account, where we have had individual accounts for ten years, my question “what do you want my Embassy to say?” drew a blank expression.

I fired off an email to Kasikorn’s HQ and they advised me there was no such requirement, they suggested I go back and ask the staff to call the number on the email, and the criteria would be explained to them.

My wife, conscious of the fact they wouldn’t like losing face, suggested we go to another branch, we did and our joint account was opened in an instant.