ER collet size chart: ER8 to ER50

Every ER collet size with the four numbers that decide whether it will fit your holder and grip your tool — plus the collapse range that most people never look up until something slips.

The numbers you actually need

Size	Clamping range (mm)	Body Ø (mm)	Length (mm)	Collapse range (mm)	Metric increment
ER8	1.0 – 5.0	8.45	13.5	0.5	0.5
ER11	1.0 – 7.0	11.5	18.0	0.5	0.5
ER16	1.0 – 10.0	17.0	27.5	1.0	1.0
ER20	1.0 – 13.0	21.0	31.5	1.0	1.0
ER25	1.0 – 16.0	26.0	34.0	1.0	1.0
ER32	2.0 – 20.0	33.0	40.0	1.0	1.0
ER40	3.0 – 26.0	41.0	46.0	1.0	1.0
ER50	6.0 – 34.0	52.0	60.0	2.0	1.0

What "collapse range" means and why it matters. Each collet grips roughly 1 mm below its nominal bore — that's how much the sleeve closes down. ER8 and ER11 only manage 0.5 mm; everything larger does about 1 mm, and ER50 about 2 mm. Fit outside that window and the collet contacts the shank only on two lines instead of gripping it, which shows up immediately as runout and then as a spinning tool in the cut.

Metric sizes you can buy per series

Series	Standard metric set	Pieces in a full set
ER8	1.0 · 1.5 · 2.0 · 2.5 · 3.0 · 3.5 · 4.0 · 4.5 · 5.0	9
ER11	1.0 · 1.5 · 2.0 · 2.5 · 3.0 · 3.5 · 4.0 · 4.5 · 5.0 · 5.5 · 6.0 · 6.5 · 7.0	13
ER16	1 – 10 in 1 mm steps	10
ER20	1 – 13 in 1 mm steps	13
ER25	2 – 16 in 1 mm steps	15
ER32	3 – 20 in 1 mm steps (2 – 20 sets also sold, 19 pc)	18–19
ER40	3 – 26 in 1 mm steps	24
ER50	6 – 34 in 1 mm steps	29

Full manufacturer table (verbatim)

This is the dimension set exactly as published to DIN 6499 form B, including the internal cone geometry columns. Reproduced unmodified — see the note under the table about what the columns mean.

Model	d H7	D	D1	D2	L	L1	L2	L3	Collapsible
ER8	1.0 – 5.0	8	8.45	6.5	13.5	2.98	1.5	1.2	0.5
ER11	1.0 – 7.0	11	11.5	9.5	18.0	3.8	2.5	2.0	0.5
ER16	1.0 – 2.5	16	17	13.8	27.5	6.26	4.0	2.7	0.5
ER16	2.5 – 10.0	16	17	13.8	27.5	6.26	4.0	2.7	1.0
ER20	1.0 – 2.5	20	21	17.4	31.5	6.36	4.8	2.8	0.5
ER20	2.5 – 13.0	20	21	17.4	31.5	6.36	4.8	2.8	1.0
ER25	1.0 – 2.5	25	26	22.0	34.0	6.66	5.0	3.1	0.5
ER25	2.5 – 16.0	25	26	22.0	34.0	6.66	5.0	3.1	1.0
ER32	2.0 – 2.5	32	33	29.2	40.0	7.16	5.5	3.6	0.5
ER32	2.5 – 20.0	32	33	29.2	40.0	7.16	5.5	3.6	1.0
ER40	3.0 – 26.0	40	41	36.2	46.0	7.66	7.0	4.1	1.0
ER50	6.0 – 10.0	50	52	46.0	60.0	12.6	8.5	5.5	1.0
ER50	10.0 – 34.0	50	52	46.0	60.0	12.6	8.5	5.5	2.0

Read the big table carefully. D1 is the external diameter of the collet body and L is overall length — those two are cross-checked against several makers and agree. D2 and L1/L2/L3 describe internal cone geometry and are reproduced verbatim from the DIN 6499 form B drawing; we have not reproduced that drawing here, so don't machine to those numbers without the original.

Per-series notes

ER8 and ER11 — the small end

Both use a 0.5 mm increment rather than 1 mm, so a full set is 9 or 13 pieces. You find them on engraving spindles, PCB mills, and 3018-class hobby routers. Their limited collapse range means they punish you more for clamping a slightly undersize shank than the larger series do.

ER16 and ER20 — the hobby workhorses

ER16 is the ceiling for most bench mills; ER20 is what ships on a lot of 6040 routers and 1.5 kW spindles. If you're building one general-purpose machine, these two cover the large majority of shank sizes hobby users actually buy.

ER25 and ER32 — routers and tool holders

ER25 is effectively the default for a 2.2 kW water-cooled spindle. ER32 crosses over into real tool holders (ISO20, BT30), which is why it's the first size where you'll also need to care about which nut thread your holder uses.

Where these numbers come from

Dimensions were compiled from published DIN 6499 form B data and cross-checked against several independent tooling manufacturers and suppliers. Points to be aware of:

Body Ø and length agree across sources, to rounding. Where sources differ (e.g. ER11 listed as 11.0 vs 11.5) the difference is nominal designation vs measured external Ø.
Minimum end of the clamping range varies by maker — some list ER16 as starting at 0.5 mm, others at 1.0 mm; ER32 is variously published as 2–20 or 3–20. Your individual collet's marking is authoritative.
Nothing here replaces your holder manufacturer's drawing. Use this to narrow down what to buy, then confirm.

Something wrong or missing? Email the correction — if it's a real error we'll fix it and note it. That's how a reference page stays trustworthy.

Collet size finder

Not sure which series your shank needs? Type the diameter and the finder lists every ER size that clamps it, with the smallest usable series first.