A cutting tool comprising a tool holder , an indexable cutting insert , and at least one clamping member , the tool holder comprising: a shank portion , and a holder portion connected to the shank portion , the holder portion having a blade-shaped front portion with an elongated supporting surface extending in a rearward-to-forward direction (D R , D F ), and the cutting insert having a central axis (A1) around which the cutting insert is indexable, and comprising: a central portion having two opposing side surfaces and three spaced apart locating surfaces extending therebetween, the central axis (A1) intersecting the two opposing side surfaces , three cutting portions connected to the central portion , each cutting portion formed between two of the three locating surfaces and including a cutting edge , and a median plane (M) located mid-way between the two opposing side surfaces of the cutting insert , the three locating surfaces defining a first imaginary triangle (T1) in a cross-section taken along the median plane (M), the cutting insert being removably securable to the holder portion in any one of three index positions by the at least one clamping member , wherein in each index position: the at least one clamping member is located entirely rearward of a first vertical plane (Pv1) containing the central axis (A1) and perpendicular to the rearward-to-forward direction (D R . D F ), and one of the three locating surfaces is in clamping contact with the supporting surface , and wherein in a direction parallel to the central axis (A1): each cutting portion has a first maximum width (W1 MAX ) defined by its cutting edge which is greater than both (i) a second maximum width (W2 MAX ) of the central portion , and also (ii) a third maximum width (W3 MAX ) of the blade-shaped front portion . a shank portion , and a holder portion connected to the shank portion , the holder portion having a blade-shaped front portion with an elongated supporting surface extending in a rearward-to-forward direction (D R , D F ), and a central portion having two opposing side surfaces and three spaced apart locating surfaces extending therebetween, the central axis (A1) intersecting the two opposing side surfaces , three cutting portions connected to the central portion , each cutting portion formed between two of the three locating surfaces and including a cutting edge , and a median plane (M) located mid-way between the two opposing side surfaces of the cutting insert , the three locating surfaces defining a first imaginary triangle (T1) in a cross-section taken along the median plane (M), the at least one clamping member is located entirely rearward of a first vertical plane (Pv1) containing the central axis (A1) and perpendicular to the rearward-to-forward direction (D R . D F ), and one of the three locating surfaces is in clamping contact with the supporting surface , and wherein in a direction parallel to the central axis (A1): each cutting portion has a first maximum width (W1 MAX ) defined by its cutting edge which is greater than both (i) a second maximum width (W2 MAX ) of the central portion , and also (ii) a third maximum width (W3 MAX ) of the blade-shaped front portion . <EOS>