Within a word, the unvoiced sound as in nothing, author or ether is often pronounced as f. Thus AAVE speakers will sometimes say nufn 'nothing' and ahfuh 'author'. The voiced sound, within a word, may be pronounced v. So 'brother' becomes bruvah, etc.
At the end of a word, th is often pronounced f in AAVE. For instance 'Ruth' is pronounced Ruf; 'south' is pronounced souf. When the preceding sound is a nasal (e.g. n or m) the th is often pronounced as t as in tent for 'tenth'; mont for 'month'.