JBMauser,
Talon is right. Those are some sort of cartridge reloading dies. They are way too thin to hold up under swaging pressure. Also, the internal threads give them away. They are for seater stems, expander ball stems, etc.
Are there any markings on them? Did the seller know anything? The .312 sizer doesn't look like anything I've ever seen but hey, if it works, super.
Paul