A two-way indexable cutting insert comprising: a regular tetrahedral basic shape defined by exactly four insert corner portions ; and four insert face surfaces mutually intersecting each other, each insert face surface being connected to three insert corner portions and spaced apart from the remaining insert corner portion , the four insert face surfaces comprising: a first rake face surface and a first relief face surface that intersect to form a first major cutting edge ; and a second rake face surface and a second relief face surface that intersect to form a second major cutting edge ; characterised in that : each of the four insert surfaces has only one rake face surface or one relief face surface , the four insert surfaces including exactly two rake face surfaces and exactly two relief face surfaces ; in a top view of the cutting insert , the cutting insert has a maximum cutting insert width (W), measured in a direction along the primary insert edge , and a maximum cutting insert length (L) measured in a direction perpendicular to the cutting insert width (W); and the maximum cutting insert length (L) is in the range W ≤ L ≤ W ∗ 1.5. a regular tetrahedral basic shape defined by exactly four insert corner portions ; and four insert face surfaces mutually intersecting each other, each insert face surface being connected to three insert corner portions and spaced apart from the remaining insert corner portion , the four insert face surfaces comprising: a first rake face surface and a first relief face surface that intersect to form a first major cutting edge ; and a second rake face surface and a second relief face surface that intersect to form a second major cutting edge ; characterised in that : each of the four insert surfaces has only one rake face surface or one relief face surface , the four insert surfaces including exactly two rake face surfaces and exactly two relief face surfaces ; in a top view of the cutting insert , the cutting insert has a maximum cutting insert width (W), measured in a direction along the primary insert edge , and a maximum cutting insert length (L) measured in a direction perpendicular to the cutting insert width (W); and the maximum cutting insert length (L) is in the range W ≤ L ≤ W ∗ 1.5. a first rake face surface and a first relief face surface that intersect to form a first major cutting edge ; and a second rake face surface and a second relief face surface that intersect to form a second major cutting edge ; characterised in that : each of the four insert surfaces has only one rake face surface or one relief face surface , the four insert surfaces including exactly two rake face surfaces and exactly two relief face surfaces ; in a top view of the cutting insert , the cutting insert has a maximum cutting insert width (W), measured in a direction along the primary insert edge , and a maximum cutting insert length (L) measured in a direction perpendicular to the cutting insert width (W); and the maximum cutting insert length (L) is in the range W ≤ L ≤ W ∗ 1.5. each of the four insert surfaces has only one rake face surface or one relief face surface , the four insert surfaces including exactly two rake face surfaces and exactly two relief face surfaces ; in a top view of the cutting insert , the cutting insert has a maximum cutting insert width (W), measured in a direction along the primary insert edge , and a maximum cutting insert length (L) measured in a direction perpendicular to the cutting insert width (W); and the maximum cutting insert length (L) is in the range W ≤ L ≤ W ∗ 1.5. <EOS>