Buying guides
How to Specify Hex Bolts: A Practical Buyer’s Checklist
Learn which hex bolt standard, thread, property class, finish and dimensions to include in an RFQ so suppliers can quote accurately.
A request for “M12 hex bolts” leaves several decisions unresolved. A reliable quotation also needs the dimensional standard, length, thread coverage, property class, material, finish and quantity.
Use this checklist to turn an informal requirement into a specification a manufacturer can verify. Reference ranges are for initial selection only; the cited standard and approved drawing control the order.
1. Start with the dimensional standard
The standard defines the geometry suppliers will inspect: head dimensions, shank form, thread length, tolerances and related details. Common metric call-outs include DIN 933 or ISO 4017 for full-thread hex bolts and DIN 931 or ISO 4014 for partial-thread products.
Standards that appear equivalent should not be silently substituted. State the exact designation shown on the drawing and identify whether an approved equivalent is acceptable.
2. Define diameter, length and thread
For metric bolts, write the nominal thread diameter and length together, such as M12 × 60. Add the pitch when a fine thread is required. For partial-thread bolts, confirm that the unthreaded grip suits the joint stack-up.
- Nominal diameter and pitch
- Length measured according to the cited standard
- Full or partial thread
- Required thread tolerance class
- Quantity split by each size
3. Separate strength, material and finish
Property class describes mechanical performance, while material and surface finish address manufacturing and corrosion requirements. Do not use these terms interchangeably. A carbon-steel class 8.8 bolt with zinc plating is a different requirement from an A2-70 stainless-steel bolt.
| RFQ field | Example | Why it matters |
|---|---|---|
| Property class | 8.8 | Controls mechanical requirements |
| Material | Carbon steel | Defines base material family |
| Finish | Zinc plated | Controls surface and corrosion requirement |
4. Add inspection and document requirements
If certificates, coating-thickness records, dimensional reports or lot traceability are required, include them before quotation. Adding documentation after production can cause delay or make an otherwise suitable lot unusable.
- Applicable standard edition
- Material or conformity certificate
- Dimensional inspection level
- Coating test requirement
- Packaging, marking and lot traceability
5. Build a quote-ready line item
A stronger line item looks like this: Hex bolt, ISO 4017, M12 × 60, coarse thread, class 8.8, zinc plated, 20,000 pieces, packed 100 pieces per box, certificate of conformity required. Add the destination and requested delivery date separately.
When a drawing conflicts with a general description, flag the conflict rather than asking the supplier to guess which requirement takes priority.
Frequently asked questions
Is DIN 933 the same as ISO 4017?
They describe closely related full-thread hex bolt forms, but dimensions and accepted tolerances should be checked against the exact editions required by the drawing.
Should bolt length include the head?
Hex bolt length is normally measured from beneath the head, but the cited product standard remains the controlling reference.
Specification note
This article is general procurement guidance. The current standard edition, approved drawing and project engineer’s requirements control the final product selection.