A bezel mandrel is the tool you use to form a bezel into a perfectly round shape before soldering it to your backing plate. If you're making a bezel by hand from strip or wire, the bezel rarely comes off the first forming attempt as a true circle. Sliding it onto the mandrel and working it down the taper corrects any oval or irregular shape and leaves you with a clean round that will sit flush when you solder it down.
This one is made from hardened tool steel with a smooth, polished surface and an even taper. The smooth finish matters because a rough or pitted surface can mark softer metals as you work them along the taper. The even taper gives you consistent gradual sizing rather than abrupt steps, which makes it easier to dial in the exact diameter you need.
Beyond bezels, this mandrel is useful for anything round and small. Jump rings, bails, clasps, and small rings can all be formed or corrected on it. The taper runs from 6.35mm to 15.88mm, which covers the range you'll work in for most bezel setting.
If you're planning to get into bezel setting stones, this mandrel belongs on your bench.
