Caliber conversion kits?

you are correct. The conversion kit includes both the shellplate, which is base dimension=specific, as well as the floating powder funnel, which is bullet diamter-specific. When you purchase an RL550B, one conversion kit is included with the machine, of a caliber you specify. Generally, you need to purchase additional conversion kits for different calibers. There is a chart at the back of the manual that outlines interchangability.

Even though there is interchangability(?) between parts of conversion kits, it is MUCH easier (for my feeble mind) to get a new conversion kit for each caliber. Keeping track of where a shell plate, funnel, locator buttons, etc came from is too much for me. I just reach over and grab the box marked (X) caliber and there they are, all in one place, organized. A little more money but well worth it IMHO. The first rule in reloading is safety and having a clean organized area is critical to this.

Mark

If you only reload one caliber, such as 308, you only need one base plate, the one for 308, but if you reload for .45, .40 S&W, 9mm, then you need one for each different caliber type.