ER20 collets
ER20 body dimensions, nominal bores and collapse ranges, accuracy grades, assembly constraints and a half-inch shank example.
Tags: tooling, interfaces, collets, toolholding
On this page
A nominal 1/2-inch (12.700 mm) shank is 0.300 mm below the upper limit of the 12.0–13.0 mm range for REGO-FIX's standard ER20 1120.13000. Its standard and UP 13 mm variants list 10 µm and 5 µm TIR respectively at the same diameter range. This nominal comparison establishes diameter fit alone. Assembly runout also depends on the holder, seating, shank and projection. REGO-FIX, standard Ø13.0 mm and related Ø1.0 mm specifications, REGO-FIX, ER20-UP Ø13.0 mm.
Body geometry and bore size
REGO-FIX's ER dimension table gives ER20 an outside diameter D1 = 21 mm and overall length L = 31.5 mm for all three listed bore bands: 1.0–1.59, 2.0–6.50 and 7.0–13.0 mm. Internal geometry varies by bore band. These are reference dimensions, not a tolerance drawing. REGO-FIX, ER System catalog, printed page 155
For comparison, the same table lists ER16 at D1 = 17 mm, usually L = 27.5 mm, but includes a 9.5–10.0 mm row at L = 26 mm; its footnote allows up to 27.5 mm depending on production. ER25 is D1 = 26 mm and L = 34 mm. Family size and bore-specific geometry both matter. REGO-FIX, dimension table, printed page 155
| Term | What it describes | ER20 example |
|---|---|---|
| Family size | Collet body and mating family | ER20 |
| Nominal bore | Named upper shank diameter of an individual collet | Ø13.0 mm |
| Clamping range | Diameters that the specified collet is documented to grip | 12.0–13.0 mm |
| Machine interface | Holder connection to the spindle | Separate from the ER20 designation |
Collapse range and accuracy are separate properties
REGO-FIX 1120.13000, standard ER20 Ø13.0 mm, lists a 13.0–12.0 mm clamping range and 0.010 mm TIR. The same product page lists the smaller 1120.01000, Ø1.0 mm, with a 1.0–0.5 mm range. The collapse span is therefore 1 mm for the former and 0.5 mm for the latter; a universal 1 mm rule would misdescribe the small collet. Collapse permits smaller shanks within the stated interval, not shanks above its upper limit. REGO-FIX, standard Ø13.0 mm and related Ø1.0 mm specifications
The 1120.13001 ER20-UP Ø13.0 mm product retains the 13.0–12.0 mm range but lists 0.005 mm TIR. UP is a distinct accuracy grade, not extra bore capacity. Both cited Ø13.0 mm products are listed as not coolant-through capable; the ER20 label alone does not establish a sealed coolant path. REGO-FIX, ER20-UP Ø13.0 mm; standard Ø13.0 mm
These product pages do not state a runout measurement distance. Their collet TIR values do not establish assembled spindle-to-cutter runout, a finished-hole tolerance or a surface-finish prediction. Engineering synthesis: holder accuracy, seating, shank geometry and projection all remain part of the assembled result.
The nut and gripping length matter
REGO-FIX mounting notice 0361.0002, marked 01/2021, describes the collet groove engaging the nut's eccentric ring before the nut/collet assembly enters the holder. Incorrect engagement can damage the nut and collet concentricity; contamination reduces clamping force and accuracy. The eccentric ring is a functional retention and extraction feature. REGO-FIX, ER Precision Tooling-System notice, pages 1–2
The notice specifies full-length shank engagement where possible, with a minimum of two-thirds of collet length. It associates insufficient insertion with permanent collet deformation and warns that bottoming against a back-up screw or holder during tightening reduces holding force and worsens runout. These are the manufacturer's assembly conditions, not a universal load rating. REGO-FIX, notice 0361.0002, page 2
Verify body fit, nut thread, nut clearance and the machine-side connection.
Worked example: a half-inch shank in a 13 mm collet
This original arithmetic assumes an ideal cylindrical 1/2-inch shank and the cited Ø13.0 mm product's 12.0–13.0 mm interval. It compares nominal diameters only:
1/2 inch = 0.500 × 25.4 = 12.700 mm
Distance below maximum = 13.000 − 12.700 = 0.300 mm
Distance above minimum = 12.700 − 12.000 = 0.700 mm
The nominal shank lies inside the interval, 0.300 mm below its maximum. In contrast, a hypothetical 13.200 mm shank exceeds the maximum by 0.200 mm; a 1 mm collapse span does not extend the range upward. Diameter membership does not predict cutting-load capacity or pullout resistance, and actual shank tolerances and engagement still matter.
As a separate geometric illustration, applying the notice's two-thirds criterion to the catalog's 31.5 mm length gives 31.5 × 2/3 = 21.0 mm. This derived minimum does not establish suitable projection or uninterrupted gripping surface.
Coverage and limitations
Use the actual assembly specification for nut torque, speed, coolant pressure, gripping force and assembled runout.
The catalog's issue date is not established here. The mounting notice itself displays 01/2021, despite later dates in its URL. The product pages show no issue date in the content reviewed on November 2, 2026; their copyright year is not a publication date.