Ok I know this is strange, but I am doing research for tax purposes for a client that has a ton of parts for AC units. I am a little bit lost on some of the items and want to know if someone can lend me their expertise. First question I have is what is a header, and what is it used for? I have various sizes, some header assemblies, and header tubes. I just need to know what those types of items are. Any input would be greatly appreciated.