Can you explain what they do, how they do it and that sort of thing. Been handloading for a while now but I don't know anything about these tools. I thought at first it was just a straight wall thing, but I see they are for bottlenecks as well. I load a variety of rifle and pistol cartridges.

red

There are a variety of case "gauges". They measure different things such as case length, headspace, bullet seating depth, etc etc. Many are made by shooters and gunsmiths when they re-barrel a rifle with a custom chamber.

Ray