Быстрый ответ
A 1/4-inch tool shank is 6.35 mm, not 6 mm. Do not force it into a collet whose maximum approved shank diameter is 6 mm. A collet with a documented range containing 6.35 mm may be suitable, but the range belongs to the exact product—not to every collet marked ER32.
This matters when a workshop uses both metric and inch tools, or when a distributor replaces a tool using a catalogue description. Check the shank size, not just the cutting diameter. An end mill’s cutting diameter and the cylindrical portion gripped by the holder can be different.
Three numbers that should stay separate
| Инструментальный шанк | Metric value | Selection check |
|---|---|---|
| 6 mm | 6.00 mm | Use a collet explicitly approved for a 6 mm shank |
| 1/4 inch | 6.35 mm | The approved range must include 6.35 mm |
| 6.5 mm | 6.50 mm | Confirm that exact diameter; do not treat it as another name for 1/4 inch |
The conversion is arithmetic: 0.25 × 25.4 = 6.35 mm. The difference from 6 mm is 0.35 mm. This calculation identifies the nominal diameter; it is not permission to exceed a collet’s limits.
Does a 7–6 mm ER32 collet cover a 1/4-inch shank?
Numerically, 6.35 mm falls inside 6–7 mm. Haas Tooling’s particular 7 mm ER32 straight-bore collet, part 04-0244, lists a 7–6 mm clamping range. It is a useful example of why the range matters. It is not proof that a different brand’s sealed, precision or special-purpose collet has the same range or suitability.
REGO-FIX explicitly warns against clamping a shank larger than the collet’s approved upper diameter. Its example rejects a 12.2 mm shank in an 11–12 mm collet and calls for a suitable larger size. Apply that upper-limit check to the actual collet in your workshop rather than assuming it can expand to accommodate an oversized tool.
The assembly information to request
Before ordering, ask for the manufacturer’s drawing or datasheet showing nominal bore, approved clamping range, suitable shank type, insertion requirement and assembly instructions. Ask separately about nut compatibility, tightening instructions, coolant sealing and the measurement conditions behind any runout claim.
If a supplier gives only “ER32 precision collet,” the request is incomplete. ER32 identifies a collet system size; it does not tell the supplier whether you intend to grip a 6 mm or 6.35 mm tool. Include the complete holder and nut codes so the proposed assembly can be checked as a set.
A purchasing checklist for mixed-unit toolboxes
- Read the tool drawing. Record cutting diameter and shank diameter in separate fields, with their original units.
- Keep the marking. Write “1/4 inch (6.35 mm)” when that is the tool specification; do not round it to 6 mm.
- Check the exact collet. Photograph its markings and obtain the approved clamping range. Measure the shank if identification is uncertain.
- Check special requirements. Note through-coolant, shank features and the precision requirement. These may narrow the choice.
- Confirm assembly instructions. The operator should follow the specific holder, nut and collet instructions before machining.
- Keep an approved pairing. Record tool, holder, nut and collet codes together after acceptance, so a repeat order does not lose the unit distinction.
A clear inquiry example
“Please quote a collet for a 1/4-inch round shank (6.35 mm), for holder [code] and nut [code]. Application: [milling/drilling]. Coolant requirement: [description]. Please state the exact collet code, approved range, assembly instructions and the documented runout measurement conditions. Quantity: [number]; destination: [country].”
For the related holder family, see BT40 ER32 toolholding. For another setup question, see our long-reach chatter checklist. Vextrex confirms the specific assembly and available options before quoting; this article does not certify any unlisted tool-and-collet combination.
Common questions
Can I tighten harder to make the wrong size work?
No. Tightening does not approve an oversized shank or replace the manufacturer’s assembly instructions. Obtain a suitable collet.
Is every ER32 collet allowed to collapse by 1 mm?
No universal allowance should be assumed. Check the exact product, especially sealed or special-purpose versions.
Manufacturer references and scope
- Haas Tooling part 04-0244: documented 7–6 mm ER32 range.
- REGO-FIX: ER assembly advice and oversized-shank warning.
References checked October 5, 2026. The inch-to-mm calculation and Vextrex purchasing checklist are stated separately from these product examples. No universal collapse range, tightening torque or runout guarantee is asserted.
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