Karats refers to the measure of purity of gold. It is commonly used to indicate the gold content in jewelry or gold objects. The clue implies that some bars can have a maximum purity of 24 karats, meaning they are made entirely of gold without any other metals mixed in.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Standards of purity. Explanations are generated by AI and may be inaccurate.