Tool Holder Types
Spindle Taper Types
| Taper | Common Names | Machine Type | Features |
|---|
| R8 | R8 | Bridgeport-style manual mills | 7/16-20 drawbar thread; simple, inexpensive; limited to lower speeds |
| CAT40 | V-Flange 40, CT40 | CNC vertical mills (North America) | 7:24 taper; V-flange with pull stud; standard in NA shops |
| CAT50 | V-Flange 50, CT50 | Large CNC mills | Larger version of CAT40; heavy roughing, large machines |
| BT30 | BT30, MAS-403 | Small CNC mills, VMCs | 7:24 taper; symmetric driving slots; lighter machines |
| BT40 | BT40, MAS-403 | CNC mills (Asia/Europe) | 7:24 taper; symmetric keyways; balanced for higher RPM than CAT40 |
| BT50 | BT50, MAS-403 | Large CNC mills (Asia/Europe) | Heavy-duty counterpart to CAT50 |
| HSK-A63 | HSK 63 | High-speed CNC mills | Hollow taper; face-and-taper contact; excellent for high RPM |
| HSK-A100 | HSK 100 | Large high-speed CNC | Larger HSK; heavy cuts at high speed; rigid connection |
| ISO 30 | INT 30, SK30 | Various milling machines | International standard; 7:24 taper |
| ISO 40 | INT 40, SK40 | Various milling machines | International standard; common in European shops |
| ISO 50 | INT 50, SK50 | Large milling machines | International standard; heavy-duty |
| MT1–MT5 | Morse Taper | Drill presses, lathes, manual mills | Self-holding taper (~5/8" per foot); ejected with drift |
| 5C | 5C Collet | Lathes, grinders, fixtures | Collet-based workholding; fast changeover; high accuracy |
CAT vs BT
CAT (V-Flange) and BT (MAS-403) holders share the same 7:24 taper angle and are dimensionally similar, but they are not interchangeable.
| Feature | CAT (V-Flange) | BT (MAS-403) |
|---|
| Drive Slots | Asymmetric V-flange | Symmetric driving slots |
| Balance | Inherently unbalanced (V-flange mass) | Symmetric = better balanced at high RPM |
| Pull Stud | Included (separate retention knob) | Separate pull stud (JIS B 6339) |
| Prevalence | North America standard | Asia & Europe standard |
| Max RPM (practical) | ~8,000–12,000 RPM | ~10,000–15,000 RPM (better balanced) |
| Interchangeable? | No — flange geometry differs; pull studs differ |
End Mill Holders
| Type | Runout (TIR) | Grip Strength | Cost | Best For |
|---|
| ER Collet Chuck | 0.0004–0.001" | Moderate | Low | General milling, versatility, quick changes |
| Shrink Fit | <0.00012" | Very High | High | High-speed finishing, precision work |
| Hydraulic | <0.00012" | High | High | Finishing, reaming, boring; vibration dampening |
| Milling Chuck (Weldon) | 0.001–0.003" | Very High | Low | Heavy roughing with Weldon-flat end mills |
| Side Lock | 0.001–0.003" | Very High | Low | Heavy roughing, drill holding |
| Heat Shrink | <0.00012" | Very High | High (requires heater) | HSM finishing, small diameter tools |
ER Collet Sizes
| System | Collet Range (mm) | Collet Range (in) | Nut Size (mm) |
|---|
| ER8 | 1–5 | 0.04–0.20" | 13 |
| ER11 | 1–7 | 0.04–0.28" | 17 |
| ER16 | 1–10 | 0.04–0.39" | 22 |
| ER20 | 1–13 | 0.04–0.51" | 26 |
| ER25 | 1–16 | 0.04–0.63" | 34 |
| ER32 | 2–20 | 0.08–0.79" | 40 |
| ER40 | 3–26 | 0.12–1.02" | 50 |
| ER50 | 6–34 | 0.24–1.34" | 63 |
Morse Taper Dimensions
| MT # | Small End (in) | Large End (in) | Length (in) | Taper/ft |
|---|
| MT0 | 0.2520 | 0.3561 | 2.00 | 0.6246 |
| MT1 | 0.3690 | 0.4750 | 2.13 | 0.5986 |
| MT2 | 0.5720 | 0.7000 | 2.56 | 0.5994 |
| MT3 | 0.7780 | 0.9380 | 3.19 | 0.6024 |
| MT4 | 1.0200 | 1.2310 | 4.06 | 0.6233 |
| MT5 | 1.4750 | 1.7480 | 5.19 | 0.6315 |
Tool Holder Selection
| Operation | Recommended Holder | Why |
|---|
| Heavy roughing | Side Lock / Weldon | Maximum grip strength prevents tool pullout under heavy loads |
| Finishing | Shrink Fit / Hydraulic | Near-zero runout for best surface finish and tool life |
| General purpose | ER Collet Chuck | Wide range of sizes, quick changeover, good balance of grip and runout |
| High-speed machining | Shrink Fit / HSK | Balanced design, low runout, secure at 15,000+ RPM |
| Drilling | Side Lock / Collet | Prevents drill spinning under thrust load |
| Reaming / boring | Hydraulic | Vibration dampening produces superior hole finish |
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