Did you hear the sad news about 12" rulers?

The joke “Did you hear the sad news about 12″ rulers? They’re not making them any longer.” plays on the double meaning of the word “longer.” In one sense, “longer” can refer to the length of an object, and in another, it can mean a continuation of an action or process. The setup leads the listener to believe there’s some unfortunate news about the production of 12-inch rulers. The punchline humorously reveals that the “sad news” is a play on words, suggesting that the rulers aren’t being made to be more extended in length, rather than not being produced anymore.