Parts, documents & AOG
Ordering screws and fasteners: thread, strength grade, finish and drawing
Turn a vague screw enquiry into a clear fastener specification: full reference, thread, length, head, material, finish, quantity and required documents.
Ask about this requirementThe quick answer
Use the complete controlled part number or drawing when one exists. If identification is incomplete, specify thread system and pitch, length convention, head/drive, material or strength class, finish and quantity as separate fields. A bolt that looks similar or screws into the same nut is not automatically an acceptable substitute. Keep proposed alternatives separate and obtain the responsible customer's technical acceptance before changing a specified standard, grade or finish.
Illustrative example — not a real customer case
A worked purchasing example: Separate size from the complete fastener requirement
An illustrative industrial drawing calls for an M6 × 1.0 screw, a specified length/head form, strength class and finish. The first enquiry says only 'M6 bolts, 100'.
What to include
- Carry the drawing reference/revision and every specified geometry/material/finish field into the request.
- Write '100 pieces' and ask suppliers to state pack size separately.
- If another finish or grade is proposed, keep it on a separate alternative line for technical review.
What this resolves
Offers can be compared on the same specification and quantity basis. The example is not an engineering selection or an aircraft part approval.
Start with the controlling identity
Send the complete part reference, standard designation and drawing revision required by your purchase specification. Preserve every prefix, suffix and dash. A supplier catalogue code and a customer drawing number may identify different things; state which is controlling. If the drawing contains an approved manufacturer list or document requirement, include that requirement rather than assuming it follows from the size. For aviation or other controlled applications, use the organisation's specified part and release-document requirements. This general fastener guide does not establish that an industrial catalogue screw is eligible for an aircraft installation.
Separate geometry, material and finish
Record metric or inch thread, nominal diameter, pitch or threads per inch, length and head style. Explain how the drawing defines length, especially where head geometry changes the reference point. Include drive type, thread length or grip requirement and any washer/nut pairing called out. Material, strength class, heat treatment and finish are separate specification fields; a change in one can affect acceptability even when the geometry matches. A photograph and measurements help identify a candidate, but cannot by themselves prove a strength grade or material condition. Mark uncertain fields instead of selecting the nearest familiar value.
Make the quotation easy to compare
Use one line per exact configuration and quantity. State whether the required quantity is pieces, packs or another explicitly defined unit, and ask the supplier to identify any minimum pack size. Keep unit price, pack quantity and total supplied pieces distinct. Attach the relevant drawing pages and list required traceability or certificates. If alternatives may be reviewed, request them as named candidates alongside the exact item, with differences stated. The final offer should clarify included documents, lead time, quantity basis and any deviation before purchase; an attractive unit price does not resolve a missing specification.
What to compare
| Specification field | Useful detail | Do not assume |
|---|---|---|
| Identity | Full P/N, standard and drawing revision | Same size means same specified part |
| Thread and length | System, pitch/TPI and drawing length convention | Metric and inch threads are interchangeable |
| Material/grade/finish | Separate required fields | Appearance proves grade or coating |
| Quantity and documents | Pieces versus packs; certificates required | A low price includes the requested pack size and documents |
Your enquiry checklist
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Common mistakes to avoid
- Inferring material or strength from a photograph
- Merging different suffixes, finishes or grades into one line
- Comparing pack prices with per-piece prices
Related products and services
Common questions
Is diameter and length enough for a fastener quote?
Usually not for an exact controlled requirement. Thread, head/drive, material or grade, finish and the applicable reference can all change what must be supplied.
Can a different strength class be offered as an upgrade?
It should be a separately identified candidate. The responsible customer or engineering authority must accept the specific change; a higher number is not a universal interchangeability rule.
What if I only have an old sample?
Send clear photographs, accessible measurements, application context and any original packaging or records. State which properties are unknown; a sample's appearance does not verify material or grade.
Sources and further reading
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