幾何戒指心軸 — 三角形鋼棒，13 吋，10 毫米至 21 毫米錐度

That triangular taper from 10mm to 21mm is perfect for sizing rings without guessing—my shanks come out evenly shaped every time. The hardened steel doesn't budge under heavy hammering, which makes forging much more controlled.

The 13-inch length gives me plenty of room to work, and the taper from 10mm to 21mm covers basically every ring size I make. Forming angle stock and heavier sheet on the flat sides feels solid, no flexing at all. My bezels come out with much cleaner corners than they did on my old round mandrel.

The triangular shape makes it so much easier to get sharp corners on ring shanks than my old round mandrel. Steel feels properly hardened, and the 10–21mm taper covers every size I actually use.