The invention relates to a turning tool comprising a basic body (1) as well as an indexable turning insert (2) having a triangular basic shape, which is fixed in an insert seat (4) in the basic body. The turning insert is formed with three side surfaces (20) that are situated in an imaginary, equilateral triangle and therefore converge in pairs at an angle of 60° toward corners in which cutting edges (22) are included. The turning insert is connected to the insert seat via an interface, which comprises, on one hand, a single active, elongate and straight engagement member (27), e.g., a ridge, and three alternately usable engagement members (28), e.g., grooves, in the turning insert. The last-mentioned members (28) are located in a second, imaginary triangle having an equilateral shape, which is smaller than the first-mentioned triangle and rotated in relation to the same.
In addition to the tool, the invention also relates to a turning insert as such.