FAQ | Xin Rui Da Fasteners

Judge by load type: ordinary static structures run fine on 8.8 (800 MPa tensile / 640 MPa yield). Under alternating loads, vibration or high reliability demands choose 10.9 (1000/940 MPa) - insufficient preload is the top fatigue-fracture cause and 10.9 tolerates higher clamp. 10.9 usually costs 20-40% more. Never mix 8.8 and 10.9 in one joint - the weaker bolts fail first.

With care. Higher strength means lower toughness: 12.9 runs 39-44 HRC, fractures brittly under shock and is more sensitive to hydrogen-delayed fracture. At impacted stations prefer 10.9 with tighter preload control per design; plated 12.9 must be de-embrittled at 190-220°C.

Not in load-bearing service. A2-70 gives 700 MPa tensile / 450 MPa yield, below 8.8 (800/640), without the 8.8 yield guarantee. Choose stainless for corrosion resistance; when you need strength and corrosion resistance together, use quenched-and-tempered alloy steel with a hydrogen-free coating such as Dacromet.

Not recommended. Keep nut grade at or above bolt grade (8.8 with grade 8, 10.9 with grade 10, 12.9 with grade 12) - otherwise the weaker internal thread strips first and the joint fails.

For the same product the three systems mostly correspond: fully threaded hex bolt DIN 933 = GB/T 5783 = ISO 4017; socket screw DIN 912 = GB/T 70.1 = ISO 4762; hex nut DIN 934 = GB/T 6170 = ISO 4032. Some DIN standards are superseded by DIN EN ISO (DIN933 → ISO 4017) with equivalent performance; supplying legacy DIN is fine, but fix the inspection standard in the contract upfront.

Do not swap systems. ASME B16.5 flanges and their bolting are a closed inch loop, and B7 diameter-strength classes are defined in the inch series (1/2"-4"). Supply inch projects from the ASTM system; metric flanges use DIN/GB 35CrMo studs. The full ANSI/ASME chart is available on request.

Same name, different part. M10 hex nut DIN934 is 17 mm across flats (ISO 4032 the same), while the M10 flange nut DIN6923 is 15 mm. Also M12 is 18 mm A/F in new standards vs 19 mm on old drawings - both producible; match by standard number, not just size.

Yes - the ASTM system pairs within families: B7 with A194 2H; sour-service B7M with 2HM (max 235 HB, 100% hardness inspected). Mixing in DIN commodity nuts breaks the hardness, capacity and traceability chain and fails petrochemical acceptance.

Common tiers: electro blue-white zinc about 48-72 h, yellow/zinc-nickel 96-240 h, hot-dip 1000 h+, Dacromet 500-1000 h+ (to red rust; industry ranges, actual depends on thickness and process). Write standard and hours into the contract, e.g. 'Dacromet, 720 h to red rust per ISO 9227'; 'zinc plated' alone binds nothing.

Three core documents: 1. Batch mill test report (heat number, chemistry, mechanicals); 2. Tensile/hardness test report per GB/T 3098.1 / ISO 898-1; 3. Finish verification (salt-spray report, coating thickness records). Petrochemical projects additionally need heat-treatment records and 100% hardness inspection (B7M/2HM). A proper supplier keeps retained samples traceable to heat number.

Acid pickling in plating drives hydrogen into the steel; high-strength Q&T parts are sensitive and may fail suddenly hours to days after assembly. The standard remedy is a 190-220°C bake right after plating - confirm the step exists in the supplier's process. Dacromet (non-electrolytic, no hydrogen uptake) is the default alternative route.

316. 304 scores PREN 18-20 (no molybdenum); 316 scores 24-26 (2-3% Mo), about 35% higher - one full environment class more pitting margin; 304 pits through in coastal salt spray. Above 60°C in chlorided water under stress, go further to duplex 2205 or nickel alloys to avoid stress-corrosion cracking.

Standard parts start from 500 pieces, and mixed multi-model containers are supported. Most new buyers trial a small container to validate quality and customs flow, then scale. Custom non-standard parts are quoted from drawings, typically 15-25 days.

Stocked lines ship in 3-7 days; custom/production runs 15-25 days. Quotations state the scheduled date per project; air freight can be arranged for urgent items. A full container cycle from contract to release - production, inspection, booking - runs roughly 1-3 weeks.

Regular stock samples are couriered immediately (freight collect typical), with dimensional/performance reports on request; newly made custom samples are calculated per drawing. Once the customer counter-signs, the sample becomes the acceptance baseline - verbal approval is where disputes start.

Most common: T/T 30% deposit + 70% against the B/L copy. After stable cooperation O/A can be discussed; large orders may use L/C. For first deals the 30/70 structure keeps risk balanced on both sides.

FOB: we deliver on board at the loading port; ocean freight and insurance are the buyer's - suits clients with their own forwarder. CIF: quote includes freight and insurance to the destination port; buyer handles clearance and inland haul. DDP: delivered-duty-paid to your door - easiest for the buyer, highest quote. Price gaps between terms are mostly freight and duties; always compare like for like.

ASEAN buyers (Vietnam, Indonesia, Thailand...) claiming FORM E or RCEP get preferential rates on most fastener lines; non-preferential markets (Middle East, South America) can use a general CO. Provide importer name, HS code (fasteners commonly under heading 7318) and contract number and we handle it; when two certificates are available, choose whichever is lower.

Customer self-inspection, SGS/BV agency inspection or factory video inspection are all supported. Agencies need 5 days' advance booking. Write AQL sampling ratio, acceptance limits and appearance reference samples into the contract so inspection has a basis.

Standard set: B/L (telex release or original), commercial invoice, packing list, and the requested certificate of origin (CO / FORM E / RCEP); batch mill certificates and test reports attach per contract. Issued 3-7 days after sailing - keep names, quantities and marks consistent with the goods to avoid clearance stalls.

The four-layer standard: inner pack in sealed VCI bags or paper; carton with PE liner plus silica gel dosed at about 1-2 g per cubic metre; export wooden crates or pallets with IPPC marks; and inside the container, 6-8 calcium chloride drying poles with dry-day stuffing only.

White rust is zinc-surface powder (basic zinc carbonate); wipe it off and the zinc remains - usually a packing-moisture cosmetic issue. Red rust means the steel substrate is attacked - water ingress or failed coating, a genuine quality problem. Pitting on stainless points to chloride-laden humidity. On arrival check whether desiccant has clumped, whether white rust wipes dry, and re-check dimensions on a sample - with the packing plan in the contract, judgement has a basis.

Yes - consolidate many models into one FCL or use LCL. Quotes list quantity, packing and shipping marks per model; loose bulk never goes into a container unprotected - condensation over 45 days defeats the best plating.

Every major destination enforces wood-packing phytosanitary rules; unmarked pallets/crates get detained at port. It is a hard requirement, and our export packing uses treated timber with the IPPC mark by default.