ER40 collets
ER40 dimensions, bore ranges, precision and sealed variants, nut engagement, and a worked inch-shank comparison.
Tags: tooling, collets, toolholding
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What ER40 identifies
REGO-FIX's 20 mm ER40 standard and UP collets both grip 19.0–20.0 mm shanks and list 10 µm and 5 µm TIR, respectively. Its 20 mm sealed DM collet lists 19.5–20.0 mm, 5 µm TIR and through-coolant capability. These are collet specifications. Confirm assembly runout and coolant sealing for the actual stack. standard 20 mm product, UP 20 mm product, DM 20 mm product.
ISO 15488:2003 covers collets with an 8° setting angle and associated holders and nuts, with separate requirements for form A and form B. ISO, ISO 15488:2003 overview.
Reference dimensions and the nut
REGO-FIX's ER catalog gives D1 = 41 mm, D2 = 40 mm and L = 46 mm for its ER40 dimensional rows, covering bore groups from 3.0 to 30.0 mm. D1, D2 and L are drawing symbols; the tool bore is the separate dimension d. Smaller-bore rows also have different internal relief dimensions. REGO-FIX, ER catalog, printed p. 155.
The same catalog lists its right-hand Hi-Q/ER40 nut 3440.00000 with an M50×1.5 thread and 63 mm outside diameter. The 3440.02000 version has a left-hand thread. These are named nut dimensions, not a claim that every ER40 nut has the same exterior or handedness. REGO-FIX, ER catalog, printed p. 109.
Thus the collet body, tool bore and nut thread are three different dimensions. Matching a bore diameter does not make an ER32 collet an ER40 component; matching a thread alone does not establish the nut's extraction and seating geometry.
Bore range and precision are product properties
The examples below are REGO-FIX products with the same nominal 20 mm bore. TIR means total indicated runout. The figures are the manufacturer's collet specifications, rather than guarantees of assembled spindle-to-cutting-edge runout.
| Variant | Part number | Published shank range | Published TIR | Coolant-through capability |
|---|---|---|---|---|
| ER40 standard | 1140.20000 | 20.0–19.0 mm | 0.010 mm | No |
| ER40-UP | 1140.20001 | 20.0–19.0 mm | 0.005 mm | No |
| ER40-DM, sealed | 1240.20000 | 20.0–19.5 mm | 0.005 mm | Yes |
Sources: standard 20 mm product, UP 20 mm product, DM 20 mm product.
The sealed example has a narrower range than the standard or UP example. “ER40” therefore supplies neither a universal 1 mm collapse range nor a universal runout grade. Coolant sealing is a separate variant feature; the table does not specify coolant pressure or qualify an entire coolant circuit.
A diameter range describes allowed shank diameters. It does not establish that a fluted section, insufficient insertion length or arbitrary surface condition provides the same grip as the intended cylindrical shank.
Assembly and contact length
REGO-FIX's ER notice describes engaging the collet groove with the nut's eccentric ring before fitting the assembly to the holder. Incorrect engagement can damage concentricity and the nut. Contamination reduces clamping force, accuracy and service life. REGO-FIX, ER precision tooling notice 0361.0002, 01/2021.
That notice calls for full-length tool insertion where possible and at least two-thirds of collet length. It also explains that a tool bottoming against a back-up screw or holder during nut tightening has poorer runout and substantially lower holding force. These are manufacturer assembly conditions, not a cutting-load rating. The notice recommends a torque wrench; a suitable nut-specific torque remains separate from spindle retention-knob torque. REGO-FIX, insertion and assembly limitations.
Worked example: a 1 inch shank
Original calculation. A nominal 1 inch cylindrical shank is 1 × 25.4 = 25.4 mm in diameter. REGO-FIX's ER40 25.5 mm standard collet, 1140.25500, has a published 25.5–24.5 mm range. The nominal shank lies inside it, 0.1 mm below the upper endpoint and 0.9 mm above the lower endpoint. REGO-FIX, 25.5 mm standard product.
The ER40 25.0 mm standard collet, 1140.25000, is listed for 25.0–24.0 mm. A 25.4 mm shank exceeds that upper endpoint by 0.4 mm. A collapse range extends toward smaller diameters; it is not permission to expand the nominal bore by the same amount. REGO-FIX, ER40 metric standard range listings.
The arithmetic addresses nominal diameter only. Actual shank tolerance, engagement, assembly cleanliness and the selected variant's requirements still affect the physical fit and holding behavior.
Coverage limits
Sources were inspected on November 2, 2026. ISO supplies the standard's edition and publication month; the ER notice prints 01/2021 despite a different year in its URL. The cited product pages and ER catalog do not establish an issue date. Search crawl dates and copyright years are not publication dates.
The public ISO abstract and manufacturer examples do not reproduce all standard tolerances or define a universal ER40 tightening torque, allowable speed, pullout force, cutting moment or coolant pressure. Collet runout specifications do not by themselves quantify the assembled holder, spindle and tool. This reference describes the interface and selected variants; it does not establish a customer's approved machining conditions.