Buyer guide
Prepared by LD Screw · Reviewed · Practical guidance for fastener RFQ preparation.
A standard number is one of the fastest ways to reduce quotation errors, but old DIN references and current ISO references are not automatically interchangeable in every detail. Check the drawing, thread length, across-flats dimension, tolerance and project requirement before approving a substitution.
Frequently requested dimensional references
These are common buyer references, not a promise that every size or variation is stocked.
| Fastener family | Common reference | Important RFQ detail |
|---|---|---|
| Partially threaded hex bolt | DIN 931 / ISO 4014 | Diameter, length, thread length, grade and finish |
| Fully threaded hex bolt | DIN 933 / ISO 4017 | Diameter, pitch, length, grade and finish |
| Threaded rod | DIN 976-1; legacy DIN 975 reference | Diameter, pitch, commercial or cut length, material and grade |
| Tap-end or double-ended stud | DIN 835 / DIN 938 / DIN 939 | Thread engagement lengths, overall length, material and drawing details |
| Hex nut | DIN 934 / ISO 4032 reference | Nut class, thread, finish and compatibility with the bolt |
| Flat washer | DIN 125 / ISO 7089 reference | Washer series, material, hardness, finish and outside diameter |
Why DIN and ISO names can cause mistakes
Buyers often use a familiar DIN number as a product name even when the purchase drawing follows an ISO edition. Small dimensional or designation differences can matter to an existing assembly.
The safest RFQ includes the required edition or drawing and identifies which dimensions are critical. If equivalence is acceptable, state that alternatives may be reviewed rather than silently substituted.
- Confirm full thread versus partial thread
- Confirm coarse or fine pitch and the required tolerance
- Confirm head dimensions, thread length and washer series
- Confirm mechanical property, stainless grade and coating separately
Standard-based RFQ checklist
A complete line item can usually be written as: standard + size + material or property class + finish + quantity + documentation.
- Attach the drawing when a critical dimension overrides the standard
- List matched nuts and washers as separate controlled items
- State whether manufacturer marking, lot traceability or test reports are required
- Add packing, labeling and destination requirements before quotation