TNMG vs CNMG Inserts — What's the Difference?

TNMG and CNMG are two of the most widely stocked turning insert families in any job shop, and it's common for buyers to treat them as interchangeable. They're not — the difference in shape changes where each insert makes sense.

Shape: triangular vs 80° rhombic

The first letter of each code tells you the shape. TNMG is triangular (60° included angle), giving three usable cutting edges per face. CNMG is 80° rhombic (diamond-shaped), giving two usable cutting edges per face. Both are negative-type inserts (the second letter, N, means 0° relief), so both are typically double-sided, doubling the edge count.

Edge strength and approach angle

The wider 80° included angle on a CNMG insert gives a stronger cutting edge at the tip, which generally holds up better under heavier roughing cuts and interrupted cuts. The narrower 60° angle on a TNMG insert is somewhat less robust at the point, but the triangular shape gives a wider range of usable approach angles on the same insert, which is useful when a single insert needs to handle several different turning profiles in one setup.

Edge count and economics

Because CNMG typically yields two edges per face (four total on a double-sided insert), while TNMG yields three per face (six total), the triangular shape can offer a lower effective cost per edge in operations where TNMG's slightly lower edge strength isn't a limiting factor.

Which one should you use?

As a starting point: reach for CNMG when you need maximum edge strength for heavier roughing or interrupted cuts, and reach for TNMG when you want more cutting edges per insert and your operation doesn't demand the extra edge strength of the 80° shape. If you're unsure, tell us your material, cut depth and whether the cut is continuous or interrupted, and we can suggest a starting point.