Quality control is the difference between fasteners that perform reliably for decades and those that fail catastrophically. Here is our comprehensive QC checklist.
Why Quality Control Matters
A single defective fastener can cause joint failure, leading to equipment damage, production downtime, or even injury. Proper QC catches problems before they reach your facility.
Dimensional Inspection
- Diameter: Check major, pitch, and minor diameters with calipers and thread gauges
- Length: Verify overall length and thread length
- Head dimensions: Across flats, across corners, head height
- Thread pitch: Verify with go/no-go gauges
- Tolerance: All dimensions must meet standard (ISO, DIN, ANSI) tolerances
Mechanical Testing
Tensile Testing
Pull test to verify the fastener meets minimum tensile strength for its grade. Record yield strength, ultimate tensile strength, and elongation.
Hardness Testing
Rockwell or Vickers hardness test on head cross-section. Must fall within the specified range for the grade.
Proof Load Test
Apply specified load for 10 seconds. Fastener must not strip or break. Verifies real-world performance.
Surface and Coating Inspection
- Visual inspection: Check for cracks, seams, laps, or surface defects
- Coating thickness: Measure with magnetic or eddy current gauge
- Coating adhesion: Tape test or bend test
- Salt spray test: Verify corrosion resistance meets specification (e.g., 500+ hours for zinc plating)
- Hydrogen embrittlement: Bake high-strength fasteners (Grade 10.9+) within 4 hours of plating
Thread Quality
- Roll threads for superior fatigue life (vs. cut threads)
- Check for burrs, nicks, or damage
- Verify thread form with optical comparator for critical applications
- Test assembly with mating nut (should assemble smoothly by hand for 2-3 threads)
Packaging and Marking
- Verify grade markings on bolt heads
- Check manufacturer identification
- Proper packaging to prevent damage during shipping
- Correct labeling with size, grade, quantity, and batch number
Documentation
Reputable suppliers provide:
- Material test certificates (EN 10204 3.1)
- Dimensional inspection reports
- Coating test reports
- Batch traceability
Our Quality Process
At Chaoshuo Trading, every shipment undergoes:
- Incoming raw material inspection
- In-process dimensional checks (every 100 pieces)
- Final inspection per AQL 2.5 standard
- Full documentation package with every shipment
Chaoshuo Trading – ISO 9001 certified. Every order includes full quality documentation. Request our QC checklist template.