Flying with Oil Pen

Hey everyone. I’ve read southwest terms on bringing an e-cigarette on the plane and it says yes, you can bring it on your carry on. My question is, can I fly with an oil pen? If I buy a new cartridge and keep it in original packaging would it be a problem? How do I go about packing it. Going from WA to Las Vegas if that helps. I’ve never been on a plane. Some people say it’s ok some people don’t! Help!