360 partially rounded head bolt help

You should be able to get a metric socket the correct size so that you have to tap it on there with a small hammer. Use the metric socket as your "in between size" , I've done it many times. When and SAE socket is too loose because a bolt head is worn out I get a metric socket that will just tap on there a little tight without busting the socket. It works every time unless the bolt is completely rounded off.

Treblig