Stainless steel hex bolts and nuts are the workhorse fasteners of structural frames, machinery, railings, food equipment and marine hardware. Selecting the right bolt and matching nut looks simple, but thread series, head style, nut type and corrosion grade each change how the joint performs. This buyer’s guide explains the common standards, thread choices and nut options to put on your RFQ.
Hex bolt standards: ISO 4014 vs ISO 4017
The metric hex head bolt family has two main dimensional standards:
- ISO 4014 (DIN 931) — partially threaded: an unthreaded shank section under the head, used when the joint has a smooth grip length and only the end engages the nut.
- ISO 4017 (DIN 933) — fully threaded: threads run almost to the head, used when the clamp stack is thin or the joint needs engagement over the full length.
In North American practice the equivalent is ASME B18.2.1 for bolts and B18.2.2 for nuts, using inch UNC/UNF threads rather than metric M dimensions.
Other common head styles
When a hex head will not clear the access space, choose a different drive:
- Socket head cap screw (ISO 4762 / DIN 912) — internal hex (Allen) drive for counterbored or recessed joints.
- Carriage bolt (DIN 603) — domed head with a square neck that bites into timber or sheet, leaving a smooth visible face.
- Hex flange bolt — integrated washer face under the head spreads bearing load on soft surfaces.
Thread: coarse vs fine pitch, metric vs inch
- Coarse metric (M standard pitch, e.g. M10×1.5) — general purpose, faster to assemble, more tolerant of slight damage, the default for most structural work.
- Fine metric (e.g. M10×1.25) — deeper effective engagement in thin walls, better vibration resistance for a given diameter, harder to cross-thread and slower to turn.
- UNC / UNF inch series — used for U.S.-spec equipment; never mix an inch bolt with a metric nut, as pitch and thread form differ and will not engage correctly.
State the exact designation, such as M12×1.75 coarse or 1/2-13 UNC, rather than just the nominal diameter.
Nut types and when to use them
- Standard hex nut (ISO 4032 / DIN 934) — general style-1 hex nut for normal structural and equipment joints.
- Thin jam nut (ISO 4035 / DIN 439) — half-height nut used to lock against another nut or in tight spaces; it is not the sole nut for a heavily loaded joint.
- Flange hex nut (ISO 4161 / DIN 6923) — built-in washer face distributes load and reduces bearing deformation on softer materials.
- Nylon-insert locknut (nyloc) — elastic nylon collar resists loosening under vibration; note it loses some holding benefit at sustained high heat.
Match washer selection and seating to the nut; our flat, spring and lock washer guide covers the companion hardware.
Grade and strength: A2-70 vs A4-80
Grade determines corrosion resistance and minimum tensile strength. Choose A2-70 (304) for general dry and indoor service, and A4-80 (316) for coastal, chloride, marine and chemical exposure. The full comparison of strength classes and what they mean on a certificate is in our A2-70 vs A4-80 fastener grade guide.
Buyer’s hex bolt and nut RFQ checklist
- Standard: ISO 4014 / ISO 4017, DIN 931 / DIN 933, or ASME B18.2.1 / B18.2.2.
- Diameter, pitch and thread series (M coarse/fine or UNC/UNF) and exact length under the head.
- Part-threaded or fully threaded, and required grip length.
- Head style: hex, socket cap, carriage or flange.
- Matching nut type: hex, jam, flange or nyloc, in the same grade.
- Grade: A2-70 or A4-80, and required passivation finish.
- Mill test certificate with chemistry and property class.
For continuous threaded joining where cut length matters, our threaded rod and stud bolt guide complements the bolt-and-nut selection.
应避免的常见错误
- Mixing metric and inch threads, or a coarse bolt with a fine nut.
- Using a thin jam nut alone in a loaded structural joint.
- Ordering full-thread ISO 4017 where a part-thread shank (ISO 4014) is specified for the grip.
- Specifying A2-70 in coastal or chloride service where A4-80 is needed.
- Ordering bolt and nut in different grades that will not match on strength.
Send us your dimensions, thread series, nut type, grade and application, and SOROYA will quote matched stainless hex bolts and nuts with the correct certification.
SOROYA PTE. LTD.
Email：nancy@soroya.com.sg
WhatsApp：+65 8058 3416
