Rapaire is right. What I thought is a hammer is, in fact, a pounder. It plainly says "16 ounces" right on the side of it. If it said "12 ounces" it would be a "three-quarter pounder".

Which brings to mind yet another question...

If the fellow in the Merle Travis song uses a nine-pound hammer, does that mean he can only pound nine times with it? What happens if what he wants to pound isn't sufficiently pounded after nine pounds? Does he have to take the nine-pound hammer back to the tool shed and fill out a requisition for a twelve-pound hammer to finish the job?

You'd think they would make hammers with more pounds in them. It must eat up a lot of the workers' time having to turn in hammers that are all pounded out. And what about the carcasses of those pounded out hammers? Do they have some way of putting pounds back in them so they can be used again, or do they just throw them away?