The letter "f" consistently makes the /f/ sound, while "v" makes the /v/ sound.
However, there are some instances where the sounds might be confused due to regional accents or differences in pronunciation. For example:
* In some dialects of English, the "f" sound at the end of words can be pronounced more like a "v", especially after a vowel. For instance, "roof" might sound more like "roo-v".
* In some languages, the letter "f" can be pronounced as a "v" sound. For instance, in Spanish, "f" is often pronounced as "v".
Let me know if you'd like to know more about how sounds in language are pronounced and how they vary between dialects!