APMT vs APKT: A Quick Comparison
This detailed guide covers the specific differences between APMT and APKT inserts, including a breakdown of the ISO tolerance classes, a dimension chart for standard sizes (1135, 1604), and specific details on the larger APMT/APKT 1705 insert.
1. The Core Difference: Tolerance Class (M vs. K)
The primary distinction is the 3rd letter of the ISO code, which dictates the manufacturing precision. This is defined by ISO 1832.
| Feature | APMT (M-Class) | APKT (K-Class) |
| Full Name | Molded Tolerance | K-Precision Ground Tolerance |
| Manufacturing | Sintered (Pressed) Carbide | Precision Ground (All sides) |
| Thickness Tolerance | ±0.13 mm (Looser) | ±0.025 mm (Very Tight) |
| Inscribed Circle (I.C.) Tolerance | ±0.05 mm to ±0.15 mm | ±0.013 mm to ±0.05 mm |
| Edge Geometry | Honed/Rounded: Stronger edge, best for roughing steel & interrupted cuts. | Sharp: Best for finishing, aluminum, and preventing chatter in long-reach tools. |
| Primary Use | Roughing, General Purpose Steel/Iron | Finishing, Aluminum, Aerospace |
Key Takeaway: The “K” class insert is ground to be almost perfectly identical in thickness. This ensures that when you install multiple inserts into a cutter, they all hit the workpiece at the exact same height, producing a smooth surface finish. “M” class inserts have slight height variations, which is fine for roughing but leaves “step lines” on a finish pass.
2. Standard Insert Dimensions (Size Chart)
The numbers following “APMT” (e.g., 1135, 1604) represent the physical dimensions.
| Insert Code | Cutting Edge Length (L) | Inscribed Circle (I.C.) | Thickness (S) | Hole Diameter (d1) | Corner Radius (r) |
| APMT 1135 | 11.3 mm | 6.35 mm (1/4″) | 3.6 mm | 2.8 mm | 0.4 – 0.8 mm |
| APMT 1604 | 17.42 mm | 9.525 mm (3/8″) | 5.2 mm | 4.4 mm | 0.8 – 1.6 mm |
| APMT 1705 | 18.5 mm | See section below | 5.56 mm | 5.0 – 5.5 mm | 0.8 – 1.2 mm |
How to Read the Dimensions (ISO Code Breakdown)
- 11 or 16: Approximate length of the cutting edge in mm.
- 03 or 04: Thickness code.
03= 3.18mm (often used in APKT 1003)35= 3.5mm (Unique to APMT 1135)04= 4.76mm05= 5.56mm
3. APMT 17 (1705) Insert Details
The APMT 1705 (often designated as APKT 1705 by brands like Iscar or TaeguTec) is a heavy-duty version of the standard 1604. It is designed for high-feed roughing and removing large amounts of material quickly.
- Why use APMT 17 over 1604?
- Thicker Body: The “05” thickness (5.56mm) is significantly thicker than the “04” (4.76mm) of the 1604 insert. This extra carbide mass prevents the insert from snapping under extreme cutting forces.
- Larger Depth of Cut: The longer edge (~17mm) allows for deeper step-downs (APMX) compared to the 1135 or 1604.
Technical Specs for APMT 1705:
- Cutting Edge Length: ~17.0 mm
- Thickness: 5.56 mm (0.218″)
- Inscribed Circle (I.C.): Typically 9.525 mm (same as 1604) or slightly larger depending on the specific “High Feed” variation.
- Screw Size: M4 or M5 (requires a larger screw than the M4 screw used in 1604 cutters).
- Compatibility: NOT interchangeable with 1604 or 1135 holders. You must use a specific “Type 17” milling cutter body.
4. Summary Recommendation
- For General Workshop Use: Buy APMT 1604 (M-Class). It is the industry standard, cheap, and handles steel/stainless roughly without breaking.
- For Aluminum or High Finish: Buy APKT 1604 (K-Class). Look for “Alu-geometry” (polished silver look) for aluminum to prevent sticking.
- For Small Mills (Desktop CNC / Bridgeport): Buy APMT 1135. The smaller cutter bodies (10mm-25mm diameter) put less strain on the spindle.
- For Heavy Roughing (Large Industrial Mills): Buy APMT 1705. Use this if you have a 40 or 50-taper mill and need to hog out material rapidly.
