Indexable carbide inserts are the disposable cutting tips that do the actual metal-cutting work on most modern lathes, mills, drills and CNC machines in Australian workshops. When one cutting edge dulls, the operator rotates the insert to a fresh edge — or replaces it entirely — without disturbing the toolholder setup. The system is faster, more consistent and more economical than brazed or regrindable tooling in any context where production volume matters.
The problem facing every machinist who buys inserts: the designation codes are dense, the brand grades don't cross-reference cleanly, and the price range from cheapest to premium is 10× to 30×. CNMG, CCMT, DCMT, TCMT, TP25, GC4325, IC8250, KCP25 — the codes look arbitrary until you understand the ISO 1832 system underneath. This guide decodes the designation system position by position, maps the major brand grades to each other, explains why prices vary so much, and shows where the SECO range stocked by AIMS fits in the Sandvik Group brand structure that dominates Australian machining.
What an indexable insert is and why machinists use them
An indexable insert is a small piece of tungsten carbide (the cutting material) shaped to a specific geometry — diamond, triangle, square, round and so on — and mechanically clamped into a steel toolholder. The insert provides the cutting edge; the toolholder provides the rigid mounting and connects to the machine spindle, turret or tool block.
The "indexable" part of the name describes the practical economy: each insert has multiple cutting edges (a square insert has 4, a triangle has 3, an 80° diamond has 4 on a negative-rake version), and when one edge wears, you rotate the insert and reuse it. Once all edges are worn, you replace the insert without removing the holder or recalibrating the setup. The holder is a long-term investment; the inserts are a consumable.
Compared to brazed carbide tools (where the carbide tip is fused to a steel shank and reground by hand when dull), indexable tooling is faster to change, more consistent edge-to-edge, and absolutely dominates production machining. Hobby and small-shop machinists sometimes still grind HSS or brazed carbide for specialised geometries — see our carbide vs HSS end mill guide for that decision — but for general turning, milling, drilling, threading and grooving, indexable inserts are the standard.
Reading the ISO 1832 designation code — position by position
ISO 1832 is the international standard that defines how every indexable insert is designated. The code is a 10-position alphanumeric string. Every major manufacturer worldwide — Sandvik Coromant, Kennametal, Iscar, Mitsubishi, SECO, Tungaloy, Walter, Sumitomo, Korloy — follows this standard for the first 10 positions, then adds their own brand-specific suffix for chipbreaker geometry and carbide grade.
Worked example for context: CNMG 120408 PR
- C = 80° diamond shape (position 1)
- N = 0° clearance angle / negative rake (position 2)
- M = medium tolerance class (position 3)
- G = hole with chipbreaker (position 4)
- 12 = 12.7 mm cutting edge length (positions 5–6)
- 04 = 4.76 mm thickness (positions 7–8)
- 08 = 0.8 mm corner radius (positions 9–10)
- PR = brand-specific chipbreaker/grade (suffix)
Position 1 — Insert shape
The first letter tells you the geometric shape of the insert and its included point angle. The shape determines how the insert behaves: stronger shapes (larger included angles) suit heavy roughing; weaker shapes (smaller included angles) suit profiling and tight corner work.
| Code | Shape | Included angle | Common use |
|---|---|---|---|
| C | 80° diamond (rhombic) | 80° | General turning, heavy roughing — the workhorse |
| D | 55° diamond (rhombic) | 55° | Profiling, contour turning, finishing |
| T | Triangle | 60° | General turning, three cutting edges per insert |
| V | 35° diamond (rhombic) | 35° | Tight profiling, plunge turning, narrow grooves |
| W | 80° trigon (modified triangle) | 80° | Roughing, high-strength turning |
| S | Square | 90° | High-strength turning, four cutting edges |
| R | Round | — | Profile turning, fine finishing, copy turning |
| K | Parallelogram (55°) | 55° | Specialty turning applications |
| P | Pentagon | 108° | Heavy turning, very strong cutting edges |
Position 2 — Clearance angle
The second letter describes the side relief angle ground into the insert. Negative-rake inserts have zero side clearance (the insert sits at an angle in the holder); positive-rake inserts have side clearance ground in. This position determines whether the insert is double-sided (more edges per insert) or single-sided (lower cutting forces).
| Code | Clearance angle | Type |
|---|---|---|
| N | 0° | Negative rake — most common, double-sided usable |
| A | 3° | Positive (small) |
| B | 5° | Positive |
| C | 7° | Positive — common on CCMT inserts |
| D | 15° | Positive — finishing applications |
| E | 20° | Positive — finishing |
| F | 25° | Positive — finishing |
| P | 11° | Positive — general purpose |
Position 3 — Tolerance class
The third letter describes how tightly controlled the insert dimensions are.
| Code | Description | Application |
|---|---|---|
| M | Medium (typical) | General production — the standard |
| G | Ground (premium) | Finishing, precision work |
| C | Class C | Finer tolerance for specialty |
Position 4 — Hole and chipbreaker
The fourth letter describes how the insert is held in the toolholder (clamping system) and whether it has a chipbreaker ground into the top face.
| Code | Description |
|---|---|
| N | No hole — clamp-on top (less common in modern tooling) |
| A | Hole, no chipbreaker |
| M | Hole + chipbreaker both sides |
| G | Hole + chipbreaker one side |
| T | Hole + chipbreaker one side, type T |
| R | Roughing geometry |
| F | Finishing geometry |
Positions 5–6 — Cutting edge length
A two-digit number giving the edge length (or inscribed circle, depending on shape) in millimetres. This determines the maximum depth of cut the insert can sustain and which toolholder size it fits.
| Code | Edge length |
|---|---|
| 06 | 6.35 mm |
| 09 | 9.525 mm |
| 12 | 12.7 mm |
| 16 | 16 mm |
| 19 | 19.05 mm |
| 25 | 25.4 mm |
Positions 7–8 — Insert thickness
A two-digit number giving the insert thickness in mm × 10 (i.e. 04 = 4.76 mm, 06 = 6.35 mm). Thicker inserts handle higher cutting forces and provide a more rigid cutting edge. The thickness code sometimes uses a letter prefix (T3 = 3.97 mm) for specific values that don't fit the standard rounded encoding.
| Code | Thickness |
|---|---|
| 02 | 2.38 mm |
| T3 | 3.97 mm |
| 03 | 3.18 mm |
| 04 | 4.76 mm |
| 06 | 6.35 mm |
Positions 9–10 — Corner radius
A two-digit number giving the nose radius of the cutting corner in mm × 10. Smaller radii produce sharper points (good for finishing and tight profile work but weaker); larger radii produce stronger corners (good for roughing and surface finish on hard materials).
| Code | Corner radius |
|---|---|
| 02 | 0.2 mm |
| 04 | 0.4 mm |
| 08 | 0.8 mm |
| 12 | 1.2 mm |
| 16 | 1.6 mm |
| 24 | 2.4 mm |
A practitioner-validated corner radius recipe from r/Machinists: "I love Sandvik and Hertel, .030 rad for rougher and .015 for finish. Maintain a good depth..." — meaning 0.8 mm corner radius (0.030″) for roughing and 0.4 mm (0.015″) for finishing as a starting point for general steel turning.
Suffix — Chipbreaker geometry and carbide grade
Everything after the standard ISO 1832 code is brand-specific. Each manufacturer uses their own letter codes for the chipbreaker geometry pressed into the top face of the insert, and their own alphanumeric codes for the carbide grade and coating. The suffix is where the brand-to-brand cross-reference becomes critical — see the dedicated section below.
ISO 513 application code — what P, M, K, N, S and H mean
ISO 513 is a separate standard that classifies cutting tool materials and their applications by workpiece material group. Every major insert manufacturer uses this colour-coded system on their grade designations so that buyers can match the grade to the work.
| ISO 513 | Material group | Colour code | Examples |
|---|---|---|---|
| P | Steel | Blue | Carbon steel, alloy steel, cast steel, ferritic stainless |
| M | Stainless steel | Yellow | Austenitic stainless, duplex, martensitic stainless |
| K | Cast iron | Red | Grey iron, nodular iron, malleable iron |
| N | Non-ferrous | Green | Aluminium, brass, bronze, copper |
| S | Heat-resistant superalloys | Brown/Orange | Inconel, titanium, nickel-based, cobalt-based |
| H | Hardened steel | Grey | Steels >45 HRC, chilled cast iron, hard-faced materials |
Within each material group, a numerical sub-classification gives the application range. Lower numbers (P10, P20) indicate grades optimised for finishing (harder substrate, more wear-resistant, less tough). Higher numbers (P40, P50) indicate grades optimised for roughing (tougher substrate, more impact-resistant, less wear-resistant). The P25 zone is the workshop sweet spot — covering general production turning and roughing.
Brand cross-reference table — grade equivalents across seven manufacturers
The single most-asked question on r/Machinists threads about inserts is some variation of "what's the [brand X] equivalent of [brand Y]?" This table maps general-purpose grade equivalents for each ISO 513 material group across the seven major brands AU machinists encounter.
| Application | SECO | Sandvik Coromant | Kennametal | Iscar | Mitsubishi | Walter | Tungaloy |
|---|---|---|---|---|---|---|---|
| Steel finishing (P10–P20) | TP1500 | GC4315 | KC5010 | IC8150 | UE6020 | WPP10 | T9015 |
| Steel general (P25) | TP25 | GC4325 | KCP25 | IC8250 | UE6110 | WPP20 | T9025 |
| Steel roughing (P30–P40) | TP3000 | GC4335 | KCP40 | IC8350 | UE6035 | WPP30 | T9035 |
| Stainless (M) | TM2000 | GC2025 | KCM25 | IC907 | VP15TF | WSM20 | T9215 |
| Cast iron (K) | TK1500 | GC3210 | KC3215 | IC5100 | UC5115 | WKK10 | T6020 |
| Heat-resistant (S) | HX | S205 | KCS10 | IC806 | VP15TF | WSP45 | T9225 |
| Aluminium (N) | F1P | GC1810 | KC410M | IC20 | NX2525 | WN10 | T1115 |
The cross-reference is at grade level — the underlying carbide chemistry and coating system. Each brand also publishes detailed chipbreaker variants within each grade (finishing, medium and roughing chip control), and those don't cross-reference one-to-one because the chipbreaker geometry is brand-specific R&D. For most general AU workshop turning, matching the grade and selecting an appropriate chipbreaker class (F1/MF2/M3 for SECO) is sufficient.
The SECO TP25 and HX grades in bold above are AIMS-stocked production-tier grades. For a Sandvik Coromant GC4325 spec, the SECO TP25 equivalent delivers the same Sandvik Group quality lineage at production-tier pricing.
Insert shape visual decoder
If you have an insert in your hand but don't know what to call it, the included point angle is the key visual feature.
| Visual | Letter | Description | Application |
|---|---|---|---|
| Wide diamond | C | 80° rhombic — most common shape worldwide | Heavy roughing turning, general production |
| Narrow diamond | D | 55° rhombic — sharper point | Profile turning, contouring, finishing |
| Equilateral triangle | T | 60° — three cutting edges | General turning, light to medium production |
| Very narrow diamond | V | 35° rhombic — sharp point | Tight profile work, plunge turning, narrow grooves |
| Modified triangle | W | 80° trigon — stronger than T | Roughing, high strength turning |
| Square | S | 90° — four cutting edges | Heavy turning, high strength |
| Circle | R | Round — continuous cutting edge | Profile, copy turning, fine finishing |
| Five-sided | P | Pentagon — 108° corners | Heavy turning, very strong edges |
Reading positive vs negative rake inserts
The clearance angle (position 2 of the ISO 1832 code) determines whether an insert is positive or negative rake — and this is one of the most consequential decisions in insert selection.
Negative rake (N = 0° clearance): The insert is double-sided. Both top and bottom faces have usable cutting edges. Common examples: CNMG, WNMG, TNMG, SNMG. A negative-rake insert with three corners (like TNMG triangle) provides 6 total cutting edges (3 corners × 2 sides). Use when:
- The setup is rigid (lathe between centres, fixture-supported workpiece)
- The depth of cut is medium to heavy
- Production volume matters — more edges per insert = lower cost-per-cut
- The cutting force pushes the workpiece into the support, not away
Positive rake (clearance letters A through F, or P): The insert is single-sided with a positive rake angle ground into the cutting edge. Common examples: CCMT, DCMT, TCMT, TPMT, VCMT. A positive-rake insert has half the usable edges of its negative counterpart. Use when:
- The setup is slender or whippy (long boring bar, small-diameter shaft)
- The depth of cut is light to medium
- Cutting force reduction matters (finishing, thin-wall work)
- Power available is limited (small lathes, hobby machines)
The 80% rule from production machining: on a rigid setup, default to negative rake for the per-insert economics. On any slender, interrupted or limited-power setup, default to positive rake for the cutting force reduction. The cost-per-cut on negative rake is roughly half that of positive rake at the same cutting performance.
Chipbreaker geometry — finishing, medium, roughing
The chipbreaker is the deliberately engineered shape on the insert's top face that controls how the chip curls and breaks. Without an effective chipbreaker, ductile materials (low carbon steel, soft stainless, aluminium) produce long stringy chips that wrap around the workpiece, jam the tool, and create a serious safety hazard. Chipbreaker geometries fall into three universal categories regardless of brand naming.
| Category | SECO | Sandvik Coromant | Kennametal | Iscar | Mitsubishi | Walter | When to use |
|---|---|---|---|---|---|---|---|
| Finishing | F1 | MF (or PF) | FN | F3M (or F3P) | FH | FP4 | Small depth of cut (0.5–2 mm), low feed (0.05–0.15 mm/rev), sharp edge, fine surface finish |
| Medium | MF2 | MM | MN | M3M | MA | MP4 | General purpose (2–4 mm DOC, 0.15–0.30 mm/rev feed), balanced edge strength and chip control |
| Roughing | M3 | MR (or PR) | RN | R3M | RH | RP5 | Heavy depth of cut (4–8 mm), high feed (0.3–0.6 mm/rev), strong edge, breaks heavy chips |
The brand naming doesn't cross-reference one-to-one in absolute performance — SECO MF2 is not identical to Sandvik MM, just both serve the medium-cut application zone. For specific operation matching, the manufacturer's catalogue chipbreaker chart is the reference.
Coating systems — PVD vs CVD, and what the colour means
Modern indexable inserts are almost universally coated — bare tungsten carbide is rare outside specialty applications. The coating provides wear resistance, thermal protection, and reduces the tendency for chips to weld to the cutting edge (built-up edge formation).
PVD (Physical Vapor Deposition) applies the coating at lower temperature (~500°C), keeping the substrate strong and the cutting edge sharp. PVD coatings are thin (typically 3–5 microns), and used for:
- Sticky materials (stainless, aluminium, soft steel) where chip welding is a concern
- Interrupted cuts where edge toughness matters
- Applications requiring sharp cutting edges (finishing, thin-wall work)
- Smaller inserts where coating thickness can't be excessive
Common PVD coatings: TiN (gold-coloured), TiCN (bronze/copper), TiAlN and AlTiN (black/dark grey), AlCrN (silver/violet-grey).
CVD (Chemical Vapor Deposition) applies thick multi-layer coatings (typically 10–25 microns) at high temperature (~1000°C), delivering superior wear resistance and thermal protection. CVD coatings are used for:
- Continuous heavy turning of steel and cast iron
- High cutting speeds where thermal load is severe
- Long production runs where total cutting life dominates economics
- Larger inserts where coating thickness contributes to wear resistance
Common CVD coatings: TiCN-Al2O3-TiN multi-layer (typical black with gold or bronze top layer).
Coating colour decoder
| Colour | Coating chemistry | Application zone |
|---|---|---|
| Gold | TiN (titanium nitride) | General purpose, finishing |
| Bronze / copper | TiCN (titanium carbonitride) | Steel and stainless wear resistance |
| Black / dark grey | TiAlN, AlTiN (aluminium titanium nitride) | High temperature, high-speed steel turning |
| Silver / violet-grey | AlCrN (aluminium chromium nitride) | Hardened steel, high heat applications |
| Black with gold top layer | CVD multi-layer (TiCN + Al2O3 + TiN) | Heavy continuous steel turning |
| Dark grey to copper | Specialty PVD multi-layer | Heat-resistant superalloys, titanium |
SECO's TP25 grade is PVD TiAlN-based — black appearance, suited to general AU workshop steel and stainless turning. SECO's TK1500 (cast iron) and TP3000 (heavy steel roughing) are CVD-coated for the continuous-cut applications where wear resistance dominates.
Why insert prices vary 5× to 20× — the quality tier reality
A general-purpose 80° diamond turning insert can cost anywhere from under three dollars from a budget Asian supplier to over thirty dollars for a premium Sandvik Coromant grade. The price difference reflects genuine differences in carbide quality, coating engineering, R&D investment and brand support — not marketing margin alone.
Tier 1 — Budget Asian inserts
Sources: eBay, AliExpress, generic Chinese imports. Pricing typically a small fraction of premium tier — useful as a benchmark for what cheap tooling looks like. Carbide quality is inconsistent batch-to-batch, coating adhesion varies, edge sharpness varies between inserts in the same pack. Forum consensus from r/Machinists: "Give the 6 flute a try, keep it strictly for roughing passes and the most you are out is..." — cheap inserts are positioned for roughing-only or disposable use. They fail predictably under production loads but can be acceptable for hobby, light-use or non-critical applications. Insert life is typically 20–30% of premium-tier equivalents.
Tier 2 — Mid-tier branded
Pricing roughly two to three times the budget tier. Brands: Korloy (Korea), ZCC-CT (China — engineered for export to European spec), Pramet (Czech), Maxigear (the hobby tier AIMS also stocks). Carbide is consistent, grades are named and documented, performance is predictable. Viable for low-volume production work, especially in non-aerospace applications. Forum consensus: respectable performance at a fraction of premium-tier cost.
Tier 3 — Production tier
Pricing typically two to three times mid-tier (and roughly half of premium-tier). Brands: SECO (Sandvik Group), Walter (United Grinding), Tungaloy (Japan), Sumitomo (Japan). R&D-backed grades, advanced coatings, engineered chipbreaker geometries. This is the tier AIMS plays in with SECO — Sandvik Group quality without Sandvik Coromant pricing. Forum consensus from r/Machinists threading thread (2 months ago): "Never had any issues with anything from Sandvik, Seco, Walter, Iscar, Vargus or Kennametal." SECO sits firmly in this proven-reliable group.
Tier 4 — Premium tier
Pricing typically 5× to 10× the budget tier (and 1.5× to 2× the production tier). Brands: Sandvik Coromant, Kennametal, Iscar, Mitsubishi. Cutting-edge metallurgy, dedicated grades for specific alloys, full technical support and engineering consultation. Premium tier pricing reflects R&D investment, brand reputation and distribution network. Pay the premium when material is expensive, deadlines are tight, or technical support matters. AIMS does not directly stock premium tier — but can source on request via the supplier network.
Within-tier brand parity reality
From r/Machinists (9 years old, still cited as definitive): "I've ran ingersoll, iscar, sandvik, dapra, and kennametal tools and they all are very close. Retooling all your machines just to change brands..."
The practitioner consensus across multiple recent threads (1–4 years old): within Tier 3 and Tier 4, performance differences between major brands are small enough that the practical decision is driven by price, availability, and the cost of retooling holders rather than absolute cutting performance. From r/Machinists CNMG-432 thread (2 years old): "Use whichever major manufacturer your shop gets the best deals on, if use Kennametal, Iscar, Ingersoll, Sandvik or Seco doesn't matter."
SECO — the Sandvik Group brand most AU machinists don't know they're buying
Sandvik AB acquired Seco Tools in 1989. Since then, SECO has operated as a separate brand within the Sandvik Group, sharing R&D infrastructure, carbide metallurgy science, and manufacturing capability with sister brand Sandvik Coromant — but positioned at production-tier pricing rather than premium-tier pricing.
For most Australian general-engineering workshop applications — turning mild steel, alloy steel, stainless, cast iron — a SECO grade like TP25 delivers Sandvik Group quality at a price point materially below Sandvik Coromant GC4325. The metallurgy is related; the R&D pedigree is the same parent company; the practical cutting performance for general workshop work is closely matched.
This matters because the Australian machining audience overwhelmingly searches for Sandvik Coromant by name (the AU keyword data shows ~200 monthly searches across all Sandvik Coromant brand variants). AIMS doesn't stock Sandvik Coromant — but does stock 1,328 SECO inserts across the full application range. The honest positioning: if a SECO grade covers the application, you are buying Sandvik Group quality without paying Sandvik Coromant pricing.
Forum-validated practitioner credibility from r/Machinists (4 years old): "I used to rock secos to rough forged A105 and sandvik..." — SECO has documented practitioner credibility on demanding materials, not just light-duty general work. The brand earns its production-tier positioning.
Reading SECO chipbreaker codes specifically
SECO uses its own chipbreaker naming inside the standard ISO 1832 framework. The three main chipbreaker codes you'll encounter on AIMS-stocked inserts:
| SECO code | Application zone | DOC range | Feed range | Practical use |
|---|---|---|---|---|
| F1 | Precision finishing | 0.25–2 mm | 0.05–0.15 mm/rev | Final surface, fine bores, light passes on slender setups |
| MF2 | Medium finishing / general production | 1–4 mm | 0.15–0.30 mm/rev | General turning, workshop default for mild steel |
| M3 | Medium roughing | 3–6 mm | 0.25–0.50 mm/rev | Heavier production cuts, alloy steel roughing |
SECO carbide grades stocked by AIMS:
- TP25 — General-purpose PVD-coated grade for steel and stainless. Covers ISO 513 P25 zone plus M area. The workshop default.
- HX — Specialty grade for heat-resistant alloys (ISO S group), titanium, high-temperature work, difficult materials.
A typical AIMS SECO turning insert designation: CCMT 09T308 MF2 TP25. Decoding: C=80° diamond shape, C=7° positive clearance, M=medium tolerance, T=hole with chipbreaker one side, 09=9.525mm edge length, T3=3.97mm thickness, 08=0.8mm corner radius, MF2=SECO medium-finishing chipbreaker, TP25=SECO general-purpose PVD-coated steel/stainless grade.
ISO 1832 across turning, milling, threading and grooving
The 10-position ISO 1832 designation system primarily covers turning inserts. Other applications use the same framework with application-specific variations.
Turning inserts
The classic ISO 1832 application — rhombic, square, round, trigon and triangle shapes for general turning, facing, profiling and boring. SECO stocks at AIMS in CCMT, DCMT, TCMT, WNMG and TNMG shapes covering the majority of general workshop applications.
Milling inserts
Milling inserts use a related ISO designation system but with different shape codes and additional considerations for the cutter body they fit. Common milling insert shapes: square (LNGU, SDET), round (RDKT), octagonal (ODHT), and specialty shapes for high-feed milling (HFMM). The cutter body sets the entry angle (45°, 90°, high-feed) — the insert provides the cutting edge.
SECO milling insert selection at AIMS depends on the specific SECO cutter body in use — match the insert designation to the cutter manufacturer's spec. Contact AIMS for assistance matching SECO milling inserts to existing toolholders.
Threading inserts
Threading inserts use ISO 5608 designation (related to but distinct from ISO 1832). Threading inserts are V-profile to match the thread form — 60° for metric and UN threads, 55° for Whitworth and BSP. Threading inserts come in full-profile (one insert produces the complete thread form) and partial-profile (multiple passes build up the form) variants.
Forum-validated quote from r/Machinists threading thread (2 months ago): "Never had any issues with anything from Sandvik, Seco, Walter, Iscar, Vargus or Kennametal." SECO threading inserts are stocked by AIMS as part of the broader range.
Parting and grooving inserts
Parting and grooving inserts use rectangular or circular geometries — the insert is wider in the direction it cuts perpendicular to the workpiece axis. Common shapes: GTN (grooving), GTAT (axial grooving), GFN (face grooving). The insert designation includes the cutting width as the primary dimension. SECO parting and grooving inserts are stocked at AIMS for cutoff and groove turning operations.
Common ISO 1832 code-reading mistakes
From forum threads documenting practical confusion points:
- Mixing up thickness (positions 7–8) with corner radius (positions 9–10). Both are two-digit numbers. The thickness comes first in the size string; the corner radius comes last. CCMT 09T308 has T3 = 3.97mm thickness and 08 = 0.8mm corner radius.
- Misreading the shape letter under poor lighting. C vs G look similar; T vs P can be confused. If in doubt, measure the included angle — that's diagnostic.
- Buying negative-rake insert for a positive-rake toolholder, or vice versa. A CNMG insert (0° negative) will not sit correctly in a CCMT toolholder (designed for 7° positive clearance). Always check the holder's insert designation, not just the shape.
- Ordering by inscribed circle (IC) when the holder spec needs edge length (L). For most ISO shapes the IC and L are different dimensions. The ISO 1832 designation positions 5–6 give edge length; the IC is a derived dimension.
- Cross-referencing brand chipbreaker codes without checking application. SECO MF2 is positioned in the medium-finishing zone but doesn't have identical chip control behaviour to Sandvik MM, Iscar M3M or Kennametal MN. Match the application class (finishing/medium/roughing) first; brand cross-reference is approximate at the chipbreaker level.
- Assuming all grades within a brand are equivalent across ISO 513 groups. SECO TP25 covers P25 and reaches into M area but isn't optimal for cast iron — for cast iron the K-series grade (TK1500) is the right answer.
- Vendor website usability frustration. Per r/Machinists Coromant thread (1 month ago): "ISCAR Kennametal and Sandvik. None of the websites are any good at all. McMaster Carr exists." The vendor SPAs are technically dense and require significant browsing to find the right insert — knowing the ISO 1832 code lets you bypass the catalogue navigation.
When cheap inserts make sense — and when they absolutely don't
The decision framework that emerges from forum threads:
Cheap inserts (Tier 1) can be acceptable when:
- Hobby or intermittent use where total cutting volume is modest
- Soft materials (mild steel, aluminium, brass) where carbide quality is less critical
- Short production runs where per-insert economics matter more than absolute performance
- Roughing operations where the cheap insert handles bulk material removal and a premium insert handles the final finish
Skip cheap inserts and pay for premium when:
- Stainless steel, hardened material, or any difficult-to-machine alloy
- High-value workpiece where scrapping the part costs more than 10× the insert
- Deadline-critical work where insert failure has cascading cost
- Production volume where total tool life dominates economics
- Surface finish requirements where edge sharpness must be predictable
The 10× rule from production machining: if the cost of scrapping a workpiece due to insert failure exceeds 10× the cost of a premium insert, always pay for the premium insert. The maths only goes one way.
AIMS SECO indexable insert range — what's stocked
AIMS stocks 1,328 SECO indexable inserts across all major machining applications — covering general engineering, production turning, milling, threading and grooving for Australian workshops.
Turning inserts — Available in CCMT, DCMT, TCMT, WNMG and TNMG ISO shapes, covering general turning, facing, boring and profiling operations. Chipbreaker styles: F1 (precision finishing), MF2 (medium finishing — the workshop default), M3 (medium roughing). Primary grades: TP25 (general-purpose PVD-coated for steel and stainless turning) and HX (heat-resistant alloys and difficult materials). The CCMT-09T308-MF2 in TP25 is the most common workshop default for general steel turning on AU lathes.
Milling inserts — Cover face milling, shoulder milling and high-feed milling applications. Correct insert selection for milling depends on the entry angle of the cutter body, depth of cut, workpiece material and the specific SECO cutter body in use. Contact AIMS for assistance matching milling inserts to existing toolholders.
Threading and parting/grooving inserts — Thread turning inserts for precision internal and external threads on CNC lathes. Parting and grooving inserts for cutoff and groove turning operations.
Maxigear hobby-tier inserts are also stocked for budget-conscious workshop applications where production-tier performance isn't required. For Tier 4 premium-tier brands (Sandvik Coromant, Kennametal, Iscar, Mitsubishi), AIMS sources on request via the supplier network — call (02) 9773 0122 or contact the team for specific premium-tier requirements.
The full SECO range at AIMS: browse indexable inserts.
Frequently Asked Questions
How do I read a carbide insert code?
Carbide inserts use the ISO 1832 designation system — a 10-position code where each position has a specific meaning. Position 1 is the insert shape (C=80° diamond, D=55° diamond, T=triangle, V=35° diamond, W=trigon, S=square, R=round). Position 2 is the clearance angle (N=0° negative, P=11° positive, etc.). Position 3 is the tolerance class (M=medium, G=ground). Position 4 is hole and chipbreaker type. Positions 5–6 are cutting edge length in mm. Positions 7–8 are thickness. Positions 9–10 are corner radius. Suffix letters indicate brand-specific chipbreaker geometry and grade. CNMG 120408 PR decodes as: C=80° diamond, N=0° negative rake, M=medium tolerance, G=hole with chipbreaker, 12=12.7mm edge length, 04=4.76mm thick, 08=0.8mm corner radius, PR=brand-specific chipbreaker/grade.
What does CNMG mean on an insert?
CNMG is the first four positions of an ISO 1832 turning insert code. C=80° diamond (rhombic) shape — the workhorse shape for general turning and heavy roughing. N=0° clearance angle (negative rake — double-sided, more cutting edges per insert, used on rigid setups). M=medium tolerance class (typical production tolerance). G=hole with chipbreaker on one side. CNMG is the most common steel turning insert configuration in production machining worldwide.
What does CCMT 09T308 mean?
CCMT 09T308 decoded: C=80° diamond shape, C=7° positive clearance angle (single-sided positive-rake insert for boring bars, slender shafts and light cuts), M=medium tolerance class, T=hole with chipbreaker one side. 09 = 9.525mm cutting edge length. T3 = 3.97mm insert thickness. 08 = 0.8mm corner radius. CCMT is the positive-rake counterpart to CNMG — used on boring bars, lighter cuts, smaller-diameter turning, and finishing work where cutting forces need to be lower.
What is the difference between Sandvik Coromant and SECO inserts?
Sandvik Coromant and SECO are both brands within the Sandvik Group — Sandvik AB acquired Seco Tools in 1989, and SECO has operated as a separate brand within the Sandvik Group ever since. They share R&D infrastructure, carbide metallurgy science, and manufacturing capability, but are positioned differently. Sandvik Coromant is the premium-tier brand at premium pricing. SECO sits at production tier — same Sandvik Group quality lineage at more competitive pricing. For most Australian general-engineering workshop turning, SECO grades like TP25 deliver Sandvik-Group quality at production-tier pricing. AIMS stocks 1,328 SECO inserts.
Are Iscar inserts compatible with Kennametal holders?
For standard ISO 1832 turning insert shapes (CNMG, CCMT, DCMT, TCMT, WNMG, TNMG and similar), inserts from different brands sharing the same ISO designation will physically fit in any holder designed for that designation. An Iscar CNMG 120408 will fit in a Kennametal CNMG holder, and vice versa. However, the chipbreaker geometry (the suffix letters) varies between brands and is not interchangeable in terms of performance. So inserts swap mechanically across brands at the ISO shape level, but you may not get the same cutting performance or chip control. Forum consensus from r/Machinists: use whichever brand your shop gets the best deals on — within top tier brands, performance is close enough that retooling cost dominates the decision.
What is ISO 1832?
ISO 1832 is the international standard that defines the designation system for indexable hardmetal (carbide) cutting inserts. It specifies a 10-position alphanumeric code where each position describes a specific physical characteristic: shape, clearance angle, tolerance class, hole/chipbreaker type, cutting edge length, thickness, corner radius, and special features. The standard is followed by all major carbide insert manufacturers worldwide so that an insert with a given designation will physically fit any toolholder designed for that designation. Brand-specific suffixes after the standard ISO 1832 code indicate chipbreaker geometry and carbide grade — these are not standardised.
What does TP25 mean as a SECO grade?
TP25 is SECO's general-purpose PVD-coated carbide grade for turning steel and stainless steel. The TP prefix designates SECO's PVD coating family. 25 indicates the application range — covering the ISO 513 P25 zone (general-purpose steel finishing to medium roughing) and extending into the M area (stainless steel). TP25 uses a PVD-applied TiAlN-based coating over a fine-grain tungsten carbide substrate. It is the workhorse grade for general AU workshop turning. Equivalent grades from other manufacturers: Sandvik Coromant GC4325, Kennametal KCP25, Iscar IC8250, Mitsubishi UE6110, Walter WPP20, Tungaloy T9025.
Why do some carbide inserts cost so much more than others?
Insert pricing reflects carbide quality, coating quality, chipbreaker engineering, and brand premium. Cheap Asian inserts (a small fraction of premium pricing) use lower-grade carbide with inconsistent quality and basic coatings. Mid-tier branded (roughly 2-3x budget tier) like Korloy and Maxigear have consistent named grades. Production-tier brands (roughly half of premium pricing) like SECO, Walter, Tungaloy, Sumitomo deliver R&D-backed performance at competitive pricing. Premium tier (5x to 10x the budget tier) like Sandvik Coromant, Kennametal, Iscar, Mitsubishi command the most for cutting-edge metallurgy. Practitioner consensus from r/Machinists: cheap inserts are 'strictly for roughing passes' and fail predictably in production work.
What is a chipbreaker on an insert?
A chipbreaker is a deliberately engineered geometry on the insert's top face — usually a series of ridges, grooves, dimples or wave forms — that controls how the chip curls and breaks as it lifts off the cutting edge. Without a chipbreaker, long stringy continuous chips form in ductile materials, which wrap around the workpiece, jam the tool, and become a safety hazard. Chipbreaker geometries fall into three application categories: finishing (small cuts, low feed, light chipbreaker like SECO F1), medium (general balance like SECO MF2), and roughing (heavy cuts, strong chipbreaker like SECO M3).
CCMT vs CNMG — what's the difference?
Both are 80° diamond shape turning inserts (the C in position 1), but they differ in clearance angle and configuration. CCMT: C-shape, C clearance (7° positive — single-sided positive-rake insert), M tolerance, T hole-with-chipbreaker. Used on boring bars, slender turning shafts, light cuts, and finishing where cutting forces must be low. CNMG: C-shape, N clearance (0° — negative rake double-sided), M tolerance, G hole-with-chipbreaker. Used for heavy turning on rigid setups — double-sided means more usable cutting edges per insert, making CNMG more economical for production work. Heavy rigid setup → CNMG; slender boring bar or light cut → CCMT.
What grade should I use for stainless steel turning?
For stainless steel turning, use a grade designed for the ISO 513 M material group. The M group requires a tougher substrate (because stainless work-hardens and is sticky) and a PVD coating that resists built-up edge formation. Grade recommendations across brands: SECO TP25 (covers M area through stainless), Sandvik Coromant GC2025, Kennametal KCM25, Iscar IC907, Mitsubishi VP15TF, Walter WSM20, Tungaloy T9215. Use a positive-rake insert geometry (CCMT or DCMT shape) where possible to reduce cutting forces and minimise work-hardening. Maintain steady feed rate — interrupted cuts on stainless dramatically accelerate insert wear.
PVD vs CVD coating — which is better?
Neither is universally better — they serve different applications. PVD (Physical Vapor Deposition) applies a thin coating (3–5 microns) at lower temperature (~500°C), preserving substrate strength and cutting edge sharpness. PVD coatings are best for sticky materials like stainless and aluminium, interrupted cuts, applications requiring sharp cutting edges. CVD (Chemical Vapor Deposition) applies thick multi-layer coatings (10–25 microns) at high temperature (~1000°C), delivering superior wear resistance and thermal protection. CVD coatings are best for continuous heavy turning of steel and cast iron, high cutting speeds, long production runs. SECO TP25 is PVD — suited to general AU workshop steel and stainless turning.
Can I cross-reference Sandvik to SECO grades?
Yes — Sandvik Coromant and SECO grades have direct equivalencies because both brands sit within the Sandvik Group. General cross-reference: Sandvik GC4325 (general steel turning) ≈ SECO TP25. Sandvik GC4335 (steel roughing) ≈ SECO TP3000. Sandvik GC2025 (stainless) ≈ SECO TM2000. Sandvik GC3210 (cast iron) ≈ SECO TK1500. Sandvik S205 (heat-resistant alloys) ≈ SECO HX. The genuine commercial story: if a SECO grade covers the application, you are buying Sandvik Group quality at production-tier pricing.
What does the M in CCMT mean?
The third letter in any ISO 1832 turning insert designation (position 3) is the tolerance class — and M designates the medium tolerance class. M is the most common tolerance class for general production machining inserts. Tighter tolerance classes exist (G = ground, C = finer) but cost more and are reserved for precision finishing. The position-3 letter is always tolerance class — so the M in CCMT, CNMG, DCMT, TCMT, TPMT, VCMT, WNMG and TNMG all mean medium tolerance.
Do I need positive or negative rake inserts?
Choose based on machine rigidity, depth of cut, and economics. Negative rake inserts (clearance angle N — e.g. CNMG, WNMG, TNMG, SNMG) are double-sided, meaning the same insert provides 2 to 4 usable cutting edges. Use negative rake when: rigid setup, heavy cuts, production work where edge-per-insert economics matter. Positive rake inserts (clearance angles A through F or P — e.g. CCMT, DCMT, TCMT) are single-sided with positive rake ground into the edge. Use positive rake when: slender or whippy workpieces, boring bars, light depth of cut, finishing work. The 80% rule: on a rigid setup default to negative rake; on slender setups default to positive rake.
What inserts does AIMS Industrial stock?
AIMS stocks 1,328 SECO indexable inserts across turning, milling, threading and parting/grooving applications. The SECO range covers the workhorse ISO turning shapes (CCMT, DCMT, TCMT, WNMG and TNMG), three chipbreaker styles (F1 for precision finishing, MF2 for medium finishing, M3 for medium roughing), and two primary carbide grades: TP25 (general-purpose PVD-coated for steel and stainless) and HX (for heat-resistant alloys and difficult materials). The milling range covers face milling, shoulder milling and high-feed milling. Premium-tier brands like Sandvik Coromant, Kennametal, Iscar and Mitsubishi are sourced on request via the supplier network. Maxigear hobby-tier inserts are also stocked. Browse the SECO range or contact AIMS for grade cross-reference advice.
Sources referenced: ISO 1832 (Indexable hardmetal inserts with rounded corners — Designation). ISO 513 (Classification and application of hard cutting materials for metal removal). r/Machinists threads (Insert Brand preferences 4yr; CNMG-432 brand preferences 2yr; Suppliers for small shops 1yr; Threading inserts 2mo; Tooling Manufacturers 7mo; Online Carbide 1yr; Good carbide lathe tools 7yr; Tooling company recommendations 1yr; Coromant Inserts 1mo). SECO Tools technical catalogue (grade families TP/TM/TK/HX/F1). Sandvik Coromant grade family reference (GC4315/GC4325/GC4335/GC2025/GC3210/S205). Kennametal, Iscar, Mitsubishi, Walter, Tungaloy grade designation references.