Rolling bearing (1) comprising an inner ring (3), an outer ring (2), at least one row of rolling elements which are arranged between raceways formed on the rings (2, 3) and a ring gear (6) that has a circumference of less than 360° and is fixed to one of the rings (2). The ring gear (6) is formed of a single gear segment (7) which has a circumference substantially equal to the circumference of the ring gear (6) and is provided on its inner or outer peripheral surface with a plurality of meshing means (7b) and fixed only to one of either the inner or outer rings (3) of the rolling bearing (1).

A power tong unit having a gear train in which one or more of the gears in the gear train have removable and replacement roller tooth elements, in lieu of conventional gear teeth. In one embodiment, the ring gear and pinion gears have roller tooth elements, and idler gears disposed between the ring gear and pinion gears, have a semi-circular tooth root profile to mesh with the roller element gear teeth. The ring gear of the power tong unit may also have a removable section. A means for removing the removable section from the ring gear, and moving it to a position in which a tubular can be inserted into a central opening in the ring gear, may include a hydraulic cylinder, a clamping mechanism, and a cam surface to generate rotation of the removable section once lifted out of engagement with the ring gear.

Rolling bearing (1) comprising an inner ring (3), an outer ring (2), at least one row of rolling elements which are arranged between raceways made on the rings (2, 3) and an ring gear (6) fixed to one of the rings (2). The ring gear (6) is formed of at least two independent gear segments (7, 8, 9, 10, 11, 12) which are each provided on their inner or outer peripheral surface with a plurality of meshing means (7b, 8b, 9b, 10b, 11b, 12b) and fixed only to one of either the inner or outer rings (3) of the rolling bearing (1), the circumference of the ring gear (6, 20) being substantially equal to the circumference of the combination of the independent gear segments.