Abstract: A milling tool includes an internal indexing mechanism arranged to displace an indexable cutting insert between an inner supported position and an outer indexing position. The indexable cutting insert has a multi-sided shape as seen in the direction of an insert centre axis and side support surfaces are included in the sides of the multi-sided indexable cutting insert. The internal indexing mechanism is arranged to provide a rectilinear movement along the shaft centre axis, between the inner supported position and the outer indexing position, wherein the indexable cutting insert is free to turn in both directions around the insert centre axis in the outer indexing position. An external indexing device for the milling tool and an indexing system is also provided. A disc member is configured with an annular geometry arranged to engage one of the side support surfaces and turn the indexable cutting insert toward the next index position.