External bone distractor

external bone distractor (1) comprising: - a rod threaded curvilinear (4) comprising bevels (7, 8) diametrically opposed preserving the threading (9) of said rod (4) according to longitudinal bands, - at least two carriages (2) hooked on said rod (4) and integral with a spindle (3), - means (10, 13) guide cooperating with said chamfers (7, 8) for locking in rotation about the axis of said rod (4), each of said carriages (2), - means (14, 15) for adjusting the position of each of said carriages (2) along said rod (4), characterized in that said bands extend only in the vicinity of the neutral fibers of said rod (4).