A preform for a microstructured fibre or a part for a preform for a microstructured fibre. The preform or part has a length in the longitudinal direction and a cross section perpendicular thereto, and includes a rod arranged at the centre of the preform or part, with one or more tubes being concentric to the rod. The rod is sleeved inside a first of the concentric tubes, and the rod and/or at least one of the concentric tubes has grooves and/or slits extending in the longitudinal direction, with the number of innermost longitudinally extending grooves and/or slits with respect to a centre of the preform or part being at least six.