ER collets ER8, ER11, ER16, ER20, ER25, ER32, ER40, ER50: collet diameter, length, clamping range and nut thread (DIN 6499 / ISO 15488) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/er-collets-er8-er50/  (sheet CC BY 4.0)
Basis: cgtk.co.uk (holder-side taper and nut thread), Little Machine Shop and RicoCNC (collet OD, length, clamping range, agree with each other), AIMS Industrial (ER8 / ER50 and maximum shank); numbers only
Catalog version: 2026-10-20

Sizes: see table below
- ER collets (DIN 6499, ISO 15488) are slotted spring collets that close in a nut; AIMS gives a nominal 1 mm clamping range for most sizes. The number is the nominal taper size in mm: ER16 sits in a holder whose taper OD is 16 mm (the cgtk column). The collet body itself is slightly larger: 11.5, 17, 21, 26, 33, 41 mm (ER32 is printed as 33 in all three sources that list lengths; one AIMS paragraph says 32), and the lengths are 18, 27.5, 31.5, 34, 40, 46 mm. Little Machine Shop, RicoCNC and AIMS agree on diameter and length for every size.
- Clamping range: Little Machine Shop and RicoCNC print 0.5–7, 0.5–9, 1–13, 1–16, 1–21, 3–26 mm for ER11 to ER40; AIMS prints a maximum shank of 7, 10, 13, 16, 20, 26 mm. The two differ at ER16 (9 / 10) and ER32 (21 / 20); both are shown and not averaged. Check your collet's own marking. The cgtk column 'taper OD / bore / minimum bore length' is the holder side as published there; the nut thread column is its nut thread diameter × pitch and thread length. cgtk notes that some ER sizes have different nut styles, so their thread need not match. ER8 and ER50 are in AIMS' table only.
- Why no files: the collet body is a slotted spring shape whose slot pattern and taper angle are not published as numbers in the sources read; a plain tube would not be a collet. Makers (Kennametal, Hoffmann, Rego-Fix, Schunk) carry 3D data on their own product pages.
- Not here: ER nut dimensions (width across flats, height, bearing-nut styles), collet slot pattern, sealed (ER-GB) collets, ER holders and tool holders per taper (see steep-taper-7-24-cat-bt-nmtb-30-40-50), and runout grades.

size  collet OD (mm)  collet length (mm)  clamping range (mm), Little Machine Shop / RicoCNC  max shank (mm), AIMS  cgtk: taper OD / bore / min bore length (mm)  nut thread (mm), cgtk  nut thread length (mm)
ER8  8.5 (AIMS)  13.6 (AIMS)  —  5 (AIMS)  —  —  —
ER11  11.5  18  0.5 – 7  7  11 / 8 / 17  14 × 0.75  8
ER16  17  27.5  0.5 – 9 (LMS, Rico)  10 (AIMS)  16 / 11 / 22  22 × 1.5  12
ER20  21  31.5  1 – 13  13  20 / 14 / 27  25 × 1.5  13
ER25  26  34  1 – 16  16  25 / 18 / 37  32 × 1.5  13
ER32  33 (a 32 appears once in AIMS' text)  40  1 – 21 (LMS, Rico)  20 (AIMS)  32 / 24 / 42  40 × 1.5  15
ER40  41  46  3 – 26  26  40 / 31 / 47  50 × 1.5  16
ER50  52 (AIMS)  60 (AIMS)  —  34 (AIMS)  —  —  —

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- cgtk.co.uk (A. S. Budden): ER collet dimensions: taper OD, bore, minimum bore length, nut thread diameter, pitch and length for ER11 to ER40 — web — Publisher's page; dimensions are facts — https://www.cgtk.co.uk/metalwork/data/er
- Little Machine Shop: ER collet sizes: length, diameter and clamping range, ER-11 to ER-40 — web — Publisher's page; dimensions are facts — https://www.littlemachineshop.com/info/er_collet_sizes.php
- RicoCNC: ER8 to ER40 collets, DIN 6499: OD, length, clamping range (agrees with Little Machine Shop) — web — Publisher's page; dimensions are facts — https://ricocnc.com/products/258-ER8-ER11-ER16-ER20-ER25-ER32-ER40-Collet-Chuck-DIN-6499-Spring-Collets.html
- AIMS Industrial: ER collet guide: ER8 to ER50 major diameter, length and maximum shank capacity — web — Publisher's page; dimensions are facts — https://aimsindustrial.com.au/blogs/product-guides/er-collet-guide
- Kennametal: ER standard collets, metric and inch (maker product pages) — web — Maker product page — https://kennametal.com/hu/en/products/p.er-standard-collets-metric.1025778.html
- Hoffmann Group: ER collet ER 16 and ER clamping nuts (maker product pages) — web — Maker product page — https://www.hoffmann-group.com/US/en/hus/p/308901-2

No true-size file yet: the published figures do not fix the whole shape; a measured scan is planned.
API: https://xemstudio.com/api/geometry?object=er-collets-er8-er50