jewel bearing

is a bearing which an unlubricated metal shaft spins in a jewel-lined pivot hole. The hole is typically shaped like a torus and is slightly larger than the shaft diameter. In operation, the shaft tilts slightly so as to contact the jewel pivot hole at two opposite points. The shaft rolls inside the bearing rather than sliding. As the shaft rolls, the center precesses.

The conical pivot (1) requires two jewels for a bearing, a cap jewel (5) and pierced jewel (6). Unlike the cylindrical pivot, the conical pivot has no "shoulder" and uses the cap jewel to determine end-shake of the wheel pinion (3). This arrangement provides lower friction than the single-jewel cylindrical pivot arrangement. Generally, friction on the conical pivot occurs only at the tip of the pinion on the lower cap jewel (3) or, in a vertical position of the watch (a horizontal position of the pinion) on the thin edges of the holes in the two pierced jewels (6).

The conical pivot is usually used on the balance wheel and, sometimes, on the escape wheel. The balance (and, when provided, escape wheel) anti-shock assembly uses a conical pivot with cap and pierced jewel.