A bearing for holding a rotary conversion tool (10, 11) that includes two end rolling bearing devices (26, 28), at least one intermediate rolling bearing device (27) interposed between the end rolling bearing devices (26, 28), the end and intermediate rolling bearing devices (26, 27, 28) being intended to engage with an end (10a, 10b, 11a, 11b) of the rotary tool (10, 11), and at least one mechanical actuator (32, 33) configured to exert a radial preload force (Fo, Fo′) at the intermediate rolling bearing device (27).