Guide · Collets and collet nuts
ER20 collets for 1/2 inch bits: sizes, makers and spindle limits
A 1/2 inch shank needs ER20 or larger. Maker ranges, single 1/2 inch collets, kits that include one, the two ER20 nut threads and the speed rule.
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Short answer
A 1/2 inch shank is 12.7 mm, and it needs an ER20 (or larger) collet made for 1/2 inch: no ER16 range checked reaches it.[1] Buy the 1/2 inch collet in your spindle's series, a nut that matches its nose thread, and stay within the speed limits the spindle and bit makers state.
Why 1/2 inch means ER20
A 1/2 inch shank is exactly 12.7 mm.[2] Galaxy and Command Tool stop their ER16 ranges at 10 mm, and Somma's ER16 list stops at 13/32 inch, about 10.3 mm. All three are below 12.7 mm.[1]
ER20 reaches it. Galaxy lists its ER20 collets with D 21.0 mm and L 31.0 mm, and its largest ER20 range is 12.0-13.0 mm.[3] Command Tool's ER20-F500 clamps 0.461-0.500 inch, about 11.7-12.7 mm, and its largest metric ER20 collet clamps 12.0-13.0 mm.[4]
Use the collet made for your shank
Pick the collet whose stated range includes your shank. For a 1/2 inch bit, the simplest match is a collet sold as 1/2 inch. REGO-FIX advises never clamping a shank larger than the collet's nominal size and moving to the next larger collet instead.[5]
Single 1/2 inch ER20 collets
Two makers in our sources sell a single ER20 1/2 inch collet:
- Haas 04-1180 is an ER20 1/2 inch straight-bore collet with a stated clamping range of 0.500-0.461 inch.[6] Haas rates it at 0.0006 inch TIR; that is the maker's claim, and the page does not say where it is measured.[6]
- CMT offers ER20 DIN6499 precision collets in 1/2 inch, 1/4 inch, 10 mm and 8 mm, each in a standard-precision and a high-precision version.[7] CMT's page does not give a measuring method for the tiers, so we do not compare them as runout figures.
Kits that already include one
If you are buying an 80 mm ER20 spindle kit, check the box first. Carbide 3D's 80 mm spindle kit includes 1/8, 1/4 and 1/2 inch ER20 collets and an ER20 nut.[8] Onefinity's 80 mm 1.5 kW Redline kit is a 110 V kit with an ER20 nut and 1/2, 3/8, 1/4 and 1/8 inch collets.[9] Its 2.2 kW kit includes the same collet sizes but is 220 V with a NEMA 6-15P plug.[10]
| Source | 1/2 in ER20 | Other sizes listed |
|---|---|---|
| Haas 04-1180 | Single collet, 0.500-0.461 in | n/a |
| CMT precision | Single collet, two tiers | 1/4 in, 10 mm, 8 mm |
| Carbide 3D 80 mm kit | Included | 1/8 in, 1/4 in |
| Onefinity 80 mm Redline kits | Included | 1/8 in, 1/4 in, 3/8 in |
Picks that fit1 product
Choose the Genmitsu ER20 14-piece set (1/16 in to 1/2 in in 1/32 in steps) for an ER20 spindle; it includes a 1/2 in collet.
More on choosing
It is collets only: use the nut that matches your spindle's ER20 thread. It does not fit ER11 or ER16.
ER20 set up to 1/2 in
Genmitsu ER20 router collet set, 14 pieces (1/16 in to 1/2 in)
The nut: ER20 alone does not identify it
PreciseBits lists standard ER20 nuts with an M25 x 1.5 thread and ER20 mini nuts with an M24 x 1.0 thread.[11] A nut sold only as "ER20" could be either. Keep the nut that came with your spindle, or check the spindle maker's documentation before ordering a spare. See ER collet nut threads and mini nuts.
A collet's range is not a speed permission
Holding a 1/2 inch shank does not mean the machine can safely spin any 1/2 inch cutter. OSHA's router guidance says tools can be flung when poorly fastened, when the wrong tool is used or when tool speed is too high, and it advises labeling tools and holders with their maximum permissible spindle speed.[12] The bit maker's speed limit and the spindle maker's instructions still apply.
Next
Questions
Which collet holds a 1/2 inch router bit?
An ER20 collet made for 1/2 inch, such as Command Tool's ER20-F500 (0.461-0.500 inch) or Haas 04-1180. ER16 does not reach 1/2 inch in any catalog checked.[4][6][1]
Is a 13 mm collet OK for a 1/2 inch shank?
Follow the collet maker's stated range. Galaxy and Command Tool list a 12.0-13.0 mm ER20 collet, and 1/2 inch is 12.7 mm, but a collet made for 1/2 inch is the direct match; if the range on the label does not include 12.7 mm, do not use it.[3][4][2]
Can my ER20 spindle run large 1/2 inch bits?
The spindle maker and the bit maker decide that, not the collet. OSHA advises labeling tools and holders with their maximum permissible speed and never running them faster.[12]
Are all ER20 nuts the same?
No. PreciseBits lists standard ER20 nuts at M25 x 1.5 and mini ER20 nuts at M24 x 1.0, so the label ER20 alone does not tell you which spindle a nut fits.[11]