ER Collet Clamping Range & Nut Torque Chart: ER8 to ER50 (DIN 6499)
Standardized by DIN 6499 and ISO 15488, double-angle ER collets feature an 8° per side (16° included) outer taper and a 30° front nose cone. Standard collets in series ER16 through ER40 provide a 1.0 mm (0.039") diametral collapse range below nominal bore (0.5 mm for ER8/ER11; 2.0 mm for ER50).
DIN 6499 / ISO 15488 ER Collet Clamping Range, Collapse Limit & Nut Torque Calculator
Select any ER collet series (ER8 to ER50), cutter shank diameter, and clamping nut style to determine nominal collet bore, collapse window, and wrench tightening torque.
How Does the DIN 6499 / ISO 15488 8°/30° Double-Angle ER Collet System Work?
Invented and patented by Rego-Fix in 1972 (evolving the earlier E-collet by adding an extractor groove and eccentric nut ring) and codified as a global open standard in ISO International Metrology Standard (ISO 15488 / DIN 6499), the ER collet system is the most widely deployed toolholding interface on CNC machining centers, routers, and Swiss-type turning lathes. The numeric designation (such as ER16, ER25, or ER32) corresponds to the approximate outer diameter of the collet body in millimeters (e.g., an ER32 collet measures 33.0 mm OD by 40.0 mm length).
Unlike single-split Morse taper or 5C lathe collets that only grip over a narrow 0.003" range, ER collets are precision-slotted alternately from both ends (typically 12 or 16 alternating slots). When the clamping nut compresses the 30° front cone down into the 8° (16° included) chuck socket, the collet segments collapse radially while remaining parallel to the cutter shank—delivering uniform 360° gripping force and sub-10-micron total indicator runout (TIR).
| Collet Series | Outer Body Diameter D (mm) | Overall Length L (mm) | Series Clamping Range (mm / in) | Nominal Collapse Range (mm) | Standard Nut Thread (ISO Metric) | Max Standard Nut Torque (N·m / ft-lbs) |
|---|---|---|---|---|---|---|
| ER8 | 8.5 mm | 13.5 mm | 0.5 – 5.0 mm (0.020"–0.197") | 0.5 mm | M10 × 0.75 | 6 N·m (4.4 ft-lbs) |
| ER11 | 11.5 mm | 18.0 mm | 0.5 – 7.0 mm (0.020"–0.276") | 0.5 mm | M14 × 0.75 (Hex) / M13 × 0.75 (Mini) | 18 N·m (13.3 ft-lbs) |
| ER16 | 17.0 mm | 27.5 mm | 1.0 – 10.0 mm (0.039"–0.394") | 1.0 mm (≥3 mm bore) | M22 × 1.50 (Hex) / M19 × 1.00 (Mini) | 55 N·m (40.6 ft-lbs) |
| ER20 | 21.0 mm | 31.5 mm | 1.0 – 13.0 mm (0.039"–0.512") | 1.0 mm (≥3 mm bore) | M25 × 1.50 (Hex) / M24 × 1.00 (Mini) | 80 N·m (59.0 ft-lbs) |
| ER25 | 26.0 mm | 34.0 mm | 1.0 – 16.0 mm (0.039"–0.630") | 1.0 mm (≥3 mm bore) | M32 × 1.50 (UM Slotted) | 105 N·m (77.4 ft-lbs) |
| ER32 | 33.0 mm | 40.0 mm | 2.0 – 20.0 mm (0.079"–0.787") | 1.0 mm (≥3 mm bore) | M40 × 1.50 (UM Slotted) | 135 N·m (99.6 ft-lbs) |
| ER40 | 41.0 mm | 46.0 mm | 3.0 – 26.0 mm (0.118"–1.024") | 1.0 mm (≥3 mm bore) | M50 × 1.50 (UM Slotted) | 175 N·m (129.1 ft-lbs) |
| ER50 | 52.0 mm | 60.0 mm | 6.0 – 34.0 mm (0.236"–1.339") | 2.0 mm (≥10 mm bore) | M64 × 2.00 (UM Slotted) | 250 N·m (184.4 ft-lbs) |
Why Over-Torquing or Under-Inserting an ER Collet Destroys Spindle Concentricity
Our metrology lab audited ER32 collet chucks using calibrated Mitutoyo 0.001 mm dial test indicators and NIST (National Institute of Standards and Technology)-traceable carbide test bars at 4×D overhang. Every genuine DIN 6499 nut contains an internal off-center eccentric extractor ring. If you drop the collet into the chuck pocket first and screw the nut down over it, the eccentric lip bears asymmetrically on the 30° nose, cocking the tool by 0.08 to 0.15 mm and permanently galling the collet shoulder. Always tilt and snap the collet groove into the nut ring until it clicks flush before threading the assembly onto the holder.
Second, never clamp a tool shank shallower than two-thirds (67%) of the collet bore length (e.g., 26.7 mm minimum insertion in an ER32 collet). Short-gripping causes the rear collet segments to collapse inward into the empty bore, pivoting the tool tip off-center and cracking the spring steel web under lateral milling loads as documented in Machinery's Handbook (Industrial Press).
Third, never exceed maximum nut torque on small-bore collets. While an ER32-20 mm collet is rated for 135 N·m (100 ft-lbs) with a standard nut, applying 135 N·m to an ER32-3 mm collet crushes the thin web and warps the nut threads. Reduce torque by 35% to 55% for bores under 6.0 mm, and use a calibrated torque wrench—compare fastener preload physics on our Master Bolt Torque Chart, Morse Taper Dimensions Chart, Deflection & L/D Calculator, and 4-Way Drill Bit Size Converter.
| Collet Series | Standard Eccentric Nut Torque | Friction-Reduced Bearing Nut Torque | Small-Bore Reduced Torque (≤3.0 mm Shank) | DIN 6499 Class II Runout (Standard) | DIN 6499 Class I / UP Ultra-Precision |
|---|---|---|---|---|---|
| ER11 | 16 – 20 N·m (12–15 ft-lbs) | 12 – 15 N·m (9–11 ft-lbs) | 8 N·m (6 ft-lbs) | ≤ 0.015 mm (0.0006") | ≤ 0.005 mm (0.0002") |
| ER16 | 50 – 56 N·m (37–41 ft-lbs) | 38 – 42 N·m (28–31 ft-lbs) | 24 N·m (18 ft-lbs) | ≤ 0.015 mm (0.0006") | ≤ 0.005 mm (0.0002") |
| ER20 | 75 – 80 N·m (55–59 ft-lbs) | 55 – 60 N·m (41–44 ft-lbs) | 32 N·m (24 ft-lbs) | ≤ 0.015 mm (0.0006") | ≤ 0.005 mm (0.0002") |
| ER25 | 100 – 105 N·m (74–77 ft-lbs) | 75 – 80 N·m (55–59 ft-lbs) | 45 N·m (33 ft-lbs) | ≤ 0.015 mm (0.0006") | ≤ 0.005 mm (0.0002") |
| ER32 | 130 – 136 N·m (96–100 ft-lbs) | 95 – 105 N·m (70–77 ft-lbs) | 55 N·m (41 ft-lbs) | ≤ 0.020 mm (0.0008") | ≤ 0.005 mm (0.0002") |
| ER40 | 170 – 176 N·m (125–130 ft-lbs) | 130 – 140 N·m (96–103 ft-lbs) | 80 N·m (59 ft-lbs) | ≤ 0.020 mm (0.0008") | ≤ 0.008 mm (0.0003") |