The phrase "brass balls" is used to describe someone who is daring, unafraid, and has a lot of courage. If you're looking for synonyms to replace this phrase, you could consider using some of the following terms: guts, nerve, balls, audacity, fearlessness, boldness, moxie, pluck, temerity, resoluteness, and determination. Each of these words encapsulates the same spirit of bravery and confidence as "brass balls." Depending on the context in which you're using the phrase, one of these synonyms might be a better fit, whether you're describing a politician who took a bold stance or a person who faced their fears head-on.