User specifically asked for this answer in the comments, so I'm copy/pasting it here. Originally written for this question.
When you have a question like this, it is best to do some minimal research to see if you can come up with a solution on your own. Lets see what Google says about "24 on center"...
The first page of results seem to imply that it has something to do with "framing" a house, and we get some suggested questions about "measuring" for 24 on center, and "studs" being on center and even "How to measure on center".
Expanding any one of those suggested questions or adding one of the additional search terms of "studs" or "measure" to your query will lead to 100s of sites that answer this very basic, fundamental question.
Community driven sites are about asking others to give up some of their time to help you with a genuine problem. When you ask questions without taking any time to research it yourself, that can be seen as selfish and wasteful.
Here are some discussions that go into more detail:
Not enough research == Not a real question?
Should a clear lack of research be grounds for closing a question?
How much research effort is expected of Stack Overflow users? StackOverflow is admittedly more strict on this, but they have 1000s of questions a day, so they have to be tighter on the rules...