An ER designation identifies a collet series; it is not the diameter of the tool shank you can put into every collet in that series. You need both the correct outer form for the holder and a bore suitable for the actual tool shank.
ER collet dimension reference
The dimensions below are a reference from the standard ER collet table in the SYIC manufacturer catalog. D refers to its d2 dimension and L to overall length. They are not a CutNexo inspection certificate or a guarantee that every catalog option has the same clamping range.
| Series | Reference D (mm) | Reference L (mm) |
|---|---|---|
| ER8 | 8.5 | 13.5 |
| ER11 | 11.5 | 18 |
| ER16 | 17 | 27.5 |
| ER20 | 21 | 31.5 |
| ER25 | 26 | 34 |
| ER32 | 33 | 40 |
| ER40 | 41 | 46 |
Four measurements to keep separate
- Series: for example ER16 or ER20, which must match the holder and nut.
- Collet dimensions: the outer form and length used to identify the series.
- Marked bore and permitted clamping interval: the size information for an individual collet.
- Tool shank: the portion actually gripped, which may differ from the cutter diameter.
A 6 mm cutter with a different shank diameter must be selected by its shank at the clamping point. Metric and imperial labels should be checked as dimensions, not treated as interchangeable names.
ER16 vs ER20: choose the assembly, then the bore
First identify the holder's series. Next confirm that the appropriate bore is available in that series and that the full assembly clears the workpiece and fixtures. A larger series is not automatically a better choice: access, holder length and the machine interface also matter. Do not install an ER16 collet into an ER20 assembly because the bore marking happens to match.
Reading CutNexo catalog options
The ER Precision Spring Collets page lists series and nominal bore combinations. For example, the current catalog contains ER16 / Bore 6 mm and ER20 / Bore 6 mm options. These are two different series, despite the shared nominal bore.
Before ordering, confirm the exact drawing, permitted clamping interval and any precision designation for the chosen option. Catalog labels alone do not establish measured runout, the full assembly accuracy or an unrestricted collapse range.
Assembly checks and selection support
Check the collet, nut and holder for correct matching and clean, undamaged contact surfaces. Follow the component manufacturer's assembly, insertion-depth and torque instructions; do not derive tightening torque from this size table.
Use the tool holder setup checklist and compare the ER collet chuck family. For selection help, send CutNexo the holder marking, collet series, tool shank diameter and required reach.