Buyer guide
Prepared by LD Screw · Reviewed · Practical guidance for fastener RFQ preparation.
DIN 933 remains a familiar name in international RFQs, while ISO 4017 is the corresponding ISO reference commonly used for fully threaded metric hexagon head screws. They describe the same general product form, but a buyer should still check the required edition, dimensions, grade, marking and project approval before accepting a substitution.
Comparison at the RFQ stage
The standard number identifies the product family; it does not complete the specification. Diameter, pitch, length, material or property class, finish and quantity must still be stated.
| Point to compare | DIN 933 direction | ISO 4017 direction |
|---|---|---|
| Product form | Metric hexagon head screw, fully threaded | Metric hexagon head screw, fully threaded |
| Reference in RFQs | Legacy DIN designation still widely used by buyers | ISO designation used in current international specifications |
| Dimensions | Check the specified edition and dimensional table | Check the specified edition and dimensional table |
| Material and strength | Must be added separately | Must be added separately |
| Substitution | Requires dimensional and project review | Requires dimensional and project review |
Why the old DIN number still appears
Part numbers, drawings, maintenance lists and distributor catalogs may keep an older DIN reference for many years. The familiar name can identify the intended product quickly, but it does not remove the need to compare the controlling dimensions and purchasing specification.
If an assembly was designed around a particular drawing or an older standard edition, verify head dimensions, width across flats, thread details and clearance before approving an ISO-referenced replacement.
- Ask which standard and edition controls the purchase order
- Check diameter, pitch, length and full-thread requirement
- Compare head dimensions and any assembly-critical clearances
- Record an approved equivalent instead of silently changing the reference
Do not confuse full thread and partial thread
DIN 933 and ISO 4017 refer to the fully threaded product form. Buyers requesting a partially threaded hex bolt commonly reference DIN 931 or ISO 4014 instead. Long lengths and special thread coverage should be checked against the standard or drawing rather than assumed from the product name.
Fine-pitch threads, left-hand threads, non-standard lengths and special head dimensions should be written explicitly in the RFQ.
- Fully threaded or partially threaded
- Coarse pitch, fine pitch or another controlled thread
- Property class or stainless material and property class
- Plain, plated, galvanized or other specified surface condition
A complete DIN 933 or ISO 4017 inquiry
A useful line item states the selected standard, nominal diameter, pitch, length, material or property class, finish and quantity. Add matched nut and washer requirements, marking, inspection documents, packing and destination when they are controlled by the project.
- Attach the buyer drawing when any dimension overrides the standard
- State whether an equivalent standard may be proposed
- Identify controlled marking, lot traceability or test documents
- Confirm sample approval and packing requirements before production