CANTON BUYING DESK Quality Control · Client Reference Material

General Quality Inspection Standard & Operating Procedure (SOP)

Applicable Scope: Cross-industry quality control (QC) practitioners and quality assurance professionals

This Standard Operating Procedure (SOP) establishes the foundational framework for quality control execution across all product categories. It defines the internationally recognized AQL sampling and disposition methodology and governs independent execution of pre-shipment inspection (OQC/PSI) at factory sites. Use in conjunction with client-issued Specification and BOM (Bill of Materials). AQL tables herein are derived from ISO 2859-1 (equivalent to ANSI/ASQ Z1.4), General Inspection Level II, normal inspection.

1. Core Philosophy of Quality Control

1.1 Ensuring Compliant Delivery

Quality Control (QC) is not an adversarial exercise in fault-finding. Its purpose is to verify that factory output conforms to client requirements and that the order can be closed out and delivered safely and compliantly.

Inspectors serve as objective gatekeepers — applying measurable standards against production output — not as punitive overseers. The mandate is compliant delivery, not dispute generation.

1.2 Core Mandate: 100% Objectivity and Transparency

Every qualified inspector operates on a single foundational principle: evidence-based reporting, data accountability, and 100% transparency.

On-site, inspectors may encounter production pressure, informal influence, or ambiguous explanations from factory personnel. Measurement instruments and documented observations constitute the sole acceptable standard. Quality data is binary — conforming or non-conforming — with no discretionary gray zone.

1.3 Key Stages of Quality Inspection

From raw material intake through finished-goods dispatch, product quality is typically governed by three sequential inspection gates:

IQC

Incoming Quality Control

Gate 1

Incoming material verification at the factory receiving point. Raw materials (fasteners, resin compounds, textiles, etc.) are inspected against specification before release to production. Non-conforming inputs invalidate all downstream output.

IPQC

In-Process Quality Control

Gate 2

In-line surveillance during assembly and production. Random checks detect equipment mis-calibration or assembly errors early, triggering line stoppage before large-batch defects accumulate.

FQC / OQC

Final / Outgoing Quality Control

Gate 3

Final verification before container loading. Finished and packed goods undergo comprehensive random inspection immediately prior to dispatch — the definitive pass/fail gate before client receipt.

2. Core Inspection Terminology

The following terms are mandatory for professional on-site communication. Cross-reference with the AQL quick-reference tables in Section 3.

2.1 AQL (Acceptable Quality Limit)

Why is it required? For a lot of 50,000 electric fans, 100% unit testing is operationally impractical in terms of time and labor.
What does it provide? AQL is the internationally recognized statistical sampling framework. It defines how many units to randomly inspect from a given lot size to achieve commercially representative quality assessment of the entire batch.
How is it applied? (Ac and Re) For each defect category within the sample, two critical values apply: Ac (Acceptance Number) — defect count ≤ Ac = Pass for that category; Re (Rejection Number) — defect count ≥ Re = Fail for that category, triggering lot rejection.

2.2 Sampling and Randomness

Sampling Compliance Protocol: Never accept units exclusively from cartons positioned at the front or top of the warehouse stack — these are frequently pre-selected “show samples.”

Stratified Random Sampling: Coverage must span front, rear, upper, lower, left, and right positions within the storage area, with carton numbers recorded. The inspector designates specific cartons: e.g., “the innermost carton on the conveyor line and the bottom-most carton in the stack.”

2.3 Defect Classification

All non-conformities identified during inspection must be classified into exactly one of the following three categories:

Defect Level	Code	Definition	Common Examples	Disposition Principle
Critical Defect	CR	Involves personal safety, regulatory non-compliance, or severe consequential risk.	Electrical leakage; exposed sharp metal on toys; outer-carton labeling violating import-market regulations.	Automatic Lot Rejection. One occurrence = entire lot Fail (AQL 0).
Major Defect	MA	Core function lost or unusable; or severe cosmetic damage likely to trigger consumer return.	Hair dryer fails to power on; table missing a leg; visible ceramic crack.	Quantity limited per AQL table; exceeding Re triggers lot rework/rejection.
Minor Defect	MI	No functional impact; cosmetic detail imperfection only.	Light scuff (≤2 mm); minor carton creasing; negligible color variance.	Permitted within AQL tolerance; exceeding Re = lot rejection.

CR · Critical

Safety, regulatory, and recall risk. Clients typically mandate AQL 0, Ac=0, Re=1.

Recommended AQL 0

MA · Major

Functional failure, significant out-of-tolerance, mislabeling. Mid-to-high value SKUs commonly use AQL 2.5.

Common AQL 2.5 / 4.0

MI · Minor

Minor cosmetic imperfections. Typically paired with MA; MI commonly set at AQL 4.0.

Common AQL 4.0 / 6.5

2.4 BOM and Specification

The client-issued Specification and BOM constitute the authoritative reference and sole legal basis for inspection. Factory statements such as “we always do it this way” are not acceptable. If the Specification defines a screw at 5 mm and field measurement yields 5.2 mm, the unit is non-conforming.

3. AQL Quick Reference: Sample Size and 2.5 / 4.0 Cross-Reference Tables

3.1 Inspection Stages: When to Apply AQL

IPC Initial Production Check At approximately 10–20% of output
Early detection of line setup errors

DUPRO During Production Inspection When finished goods and packaging reach approximately 10%–30%
Early corrective action to prevent batch-wide defects

PSI / FRI / OQC Pre-Shipment / Final Random Inspection Principally ≥80% packed (100% recommended) before inspection commences
Final disposition prior to payment and container loading

Note: IPC/DUPRO and PSI/OQC have distinct readiness thresholds. Do not apply pre-shipment packaging-ratio requirements to mid-production inspections.

3.2 Lot Size → Sample Code Letter → Sample Size (n)

The following tables apply to General Inspection Level II, normal inspection. Determine the code letter from lot size, then reference Ac/Re below. Tightened or reduced inspection alters the code letter and must be documented in the Quality Agreement (QA).

Lot Size (units)	Code Letter	Sample Size n	Lot Size (units)	Code Letter	Sample Size n
2 – 8	A	2	501 – 1,200	J	80
9 – 15	B	3	1,201 – 3,200	K	125
16 – 25	C	5	3,201 – 10,000	L	200
26 – 50	D	8	10,001 – 35,000	M	315
51 – 90	E	13	35,001 – 150,000	N	500
91 – 150	F	20	150,001 – 500,000	P	800
151 – 280	G	32	500,001+	Q	1,250
281 – 500	H	50	Source: ISO 2859-1 Table I

Table A — Critical Defects CR (AQL 0 · Zero Tolerance)

Sample Size n	Accept Ac	Reject Re	Disposition Rule
All sample sizes	0	1	≥ 1 CR → entire lot Fail, regardless of MA/MI results

Table B — Major Defects MA · AQL 2.5 (Stringent — mid-to-high value SKUs)

Defect count ≤ Ac → Pass for that category Defect count ≥ Re → Fail for that category Between Ac and Re: apply Re rule (Fail)

Sample Size n	Ac	Re	Sample Size n	Ac	Re
2	0	1	80	5	6
3	0	1	125	7	8
5	0	1	200	10	11
8	0	1	315	14	15
13	1	2	500	21	22
20	2	3	800	21	22
32	3	4	1,250	21	22
50	5	6	ISO 2859-1 Table II-A, single normal inspection

Table C — Major Defects MA · AQL 4.0 (Standard — promotional / high-volume lots)

Sample Size n	Ac	Re	Sample Size n	Ac	Re
2	0	1	80	7	8
3	0	1	125	10	11
5	0	1	200	14	15
8	1	2	315	21	22
13	2	3	500	21	22
20	3	4	800	21	22
32	5	6	1,250	21	22
50	5	6	ISO 2859-1 Table II-A, single normal inspection

Table D — Minor Defects MI · AQL 4.0 (commonly paired with MA AQL 2.5)

Sample Size n	Ac	Re	Sample Size n	Ac	Re
13	3	4	125	14	15
20	5	6	200	21	22
32	7	8	315	21	22
50	7	8	500+	21	22
80	10	11	Low-risk categories may use MI AQL 6.5 — must be specified in QA

Industry-standard combination: CR = AQL 0; MA = AQL 2.5; MI = AQL 4.0. Each category must be counted and dispositioned independently; any single category Fail = entire lot Fail.

Technical Note: If the client QA specifies a non-standard AQL combination (e.g., MA AQL 1.5 / MI AQL 4.0), different defect categories may yield inconsistent sample sizes (n). In such cases, visual inspection must use the larger of the calculated sample sizes.

3.3 Worked Example: Lot of 2,000 units, MA AQL 2.5

Step 1: Lot size 2,000 units → code letter K → sample size n = 125 (stratified random draw from packed cartons).

Step 2: MA (AQL 2.5): Ac = 7, Re = 8. If 6 MA defects are found → category Pass.

Step 3: CR (AQL 0): If 1 CR defect is found → entire lot Fail, even if MA count (6) satisfies Pass criteria.

Conclusion: CR, MA, and MI must be counted and table-referenced separately. Any category triggering Re = lot rejection.

4. Supplementary Inspection Protocols (Field Essentials)

Master Sample / Approved Reference Sample

Client-approved reference unit for color, material, and finish comparison. In the absence of an approved sample, the Specification governs.

First Article Inspection (FAI)

Comprehensive verification of the first production unit(s) before mass run authorization. FAI sign-off is mandatory before batch release; deviations require line adjustment.

Hold and CAPA

Upon inspection Fail, shipment must be suspended pending factory submission of Corrective and Preventive Action (CAPA): root cause, countermeasure, responsible party, and completion date, followed by re-inspection.

Quarantine Zone

Non-conforming units must be physically segregated from conforming stock, clearly red-tagged, and prohibited from co-mingling or loading. Re-inspection clearance required before release to shipment lot.

Standard Illuminant D65

Visual and color-difference inspection must be conducted under agreed light source conditions (commonly D65, ~6500K). Avoid assessment under dim warehouse lighting or color-skewed lamps.

Inspection Readiness Conditions (Stage-Specific)

DUPRO (During Production): International practice permits inspection when finished goods are produced and packaging is approximately 10%–30% complete — enabling early detection of line/process defects before large-batch accumulation.
PSI / FRI / OQC (Pre-Shipment): The ≥80% packed threshold (100% recommended) applies exclusively to pre-shipment inspection. If substantial volume remains unboxed on the production line, pre-shipment inspection should not commence. Total carton count must reconcile with delivery documentation before inspection begins.

Stratified Random Sampling

Draw cartons from front, middle, and rear stack positions at multiple elevation levels. Record carton numbers, seal numbers, and timestamps. Reject factory-offered pre-selected cartons.

Loading Supervision

Verify carton count, seal numbers, and loading sequence; capture photographic/video evidence. Prevents post-inspection carton substitution, short-shipment, or co-mingling of other order goods.

4.1 Packaging and On-Site Test Protocols

Readiness Threshold Reminder: Most tests in this section (drop test, carton weight verification, barcode scan) apply to packed finished goods and are typically executed at the PSI / OQC stage. For DUPRO, inspection may commence at approximately 10%–30% packaging completion per QA agreement. The ≥80% packed requirement applies strictly to final pre-shipment inspection.

Outer Carton Markings and Labels — Print content, language, and barcodes must match PO/Specification; barcodes must scan and read correctly.

Unit / Carton Weight Verification — Gross and net weight within Specification tolerance; abnormally low weight may indicate missing components or material substitution.

Drop Test — Free-fall from height per client or ISTA protocol; verify inner packaging integrity and post-drop functional performance.

Cross-Hatch / Tape Adhesion Test — Coating and print adhesion; apply specified tape (e.g., 3M) and record peel-off grade.

Functional Test — Operate as an end consumer would: power on/off, assembly, electrical test (dry hands), runtime, etc.; record defect unit numbers and photographs.

4.2 Inspection Report Documentation Standards

Reports must be objective and auditable. Avoid subjective language (“appears acceptable,” “approximately”). Apply the standard defect description formula:

Defect Description Standard Formula: Defect Description = Location + Symptom + Severity / Specific Data

Recommended report structure:

Basic Information: Factory, PO, product, lot size, inspection date, sample n, AQL values per agreement.
Sampling Record: Carton draw locations, carton number list, inspection stage (DUPRO / PSI, etc.), and packaging completion percentage at time of inspection.
Results Summary: CR / MA / MI counts, cross-referenced against Ac/Re, with Pass or Fail per category.
Defect Descriptions (per standard formula): Quantity + location + symptom + data/grade + photo reference. Example: “Of 125 units sampled, 3 units exhibited [visible scratching (symptom)] at [2 cm right of front logo (location)], each measuring [approximately 5 mm in length, exceeding MA limit (specific data)] (Photo Ref. 03).”
On-Site Acknowledgment: Non-conformities must be reviewed and signed by factory quality representative on-site; photographs must include defect close-ups and carton markings.

5. Standard 5-Step On-Site Inspection Protocol

When executing pre-shipment inspection (OQC/PSI) independently, follow this five-step sequence to minimize omissions and ensure consistent execution.

Step 1: Pre-Inspection Readiness & Instrumentation → Step 2: Carton Opening & Unit Count → Step 3: Visual & Functional Testing → Step 4: Data Analysis & Disposition → Step 5: Communication & Reporting

Step 1: Pre-Inspection Readiness

Document Alignment — Print BOM, Specification, and AQL tables; carry client master/approved sample (if applicable).

Measuring Instruments — Digital caliper, 2 m / 5 m tape measure (verify caliper battery charge).

Weighing and Recording — Handheld electronic scale, precision gram scale, camera/phone, notebook, marker pen (for marking sampled carton numbers).

Specialized Tools — 3M tape (cross-hatch/barcode test), power bank.

Step 2: On-Site Carton Opening and Unit Count

Lot Verification — Reconcile total carton count against delivery note/invoice; for pre-shipment inspection (PSI/OQC), do not commence if unboxed ratio is excessive (principally requires ≥80% packed); for DUPRO, approximately 10%–30% packed per QA agreement is sufficient.

Sample Size Calculation — Derive n from lot size via code letter table; determine number of cartons to draw (stratified random).

Carton Designation — Specify carton numbers directly (e.g., cartons 5, 48, 112); reject handler pre-selection; supervise transport to inspection station.

Step 3: Visual and Functional Testing

Packaging Information — Markings, labels, barcode scan, and content consistency verification.

Visual Inspection — Under standard illuminant, viewing distance approximately 30–40 cm, front/top/side angles; check for scratches, stains, color variance, burrs.

Dimensions and Weight — Critical dimensions measured with caliper; unit weight and carton gross weight recorded.

Functional Verification — Buttons, assembly, drop test, etc., per Specification.

Step 4: Data Compilation and Disposition

Aggregate CR, MA, and MI counts; cross-reference each against corresponding AQL table Ac/Re values.

Example: MA AQL 2.5, n=80 → Ac=5, Re=6; MA=4 → Pass; MA=6 → Fail.

Any category triggering Re → entire lot Fail; all categories within Ac → Pass.

Step 5: On-Site Communication and Reporting

Non-Conformance Acknowledgment — Immediately present defects to quality supervisor/plant manager for on-site verification, signature, and photographic record.

Written Report Completion — Complete per Section 4.2 structure, with clear defect photographs and carton number records.

6. Field Operational Best Practices

6.1 Handling On-Site Discrepancies & Factory Disputes

Common factory statements: “This minor mark doesn’t affect function” or “The vessel is departing — are you responsible if we miss it?”

Protocol: Maintain professional composure and hold to documented standards. Recommended response: “I understand the shipment schedule is critical. My responsibility is to report findings accurately to the client; release authorization rests with the client. Let us first verify the dimensional and visual data together.” — Redirect decision authority to the Specification and client; refocus on measurable data.

6.2 Workplace Safety (EHS)

Use designated walkways; remain alert to forklift alarms and rear traffic.

Wear safety footwear and hard hat in mechanical/heavy-industry production areas.

Ensure dry hands before electrical testing to prevent shock hazard.

Mechanical Safety Protocol: Never insert hands or any body part into operating machinery without factory authorization and appropriate safety measures (Lockout/Tagout).

6.3 Field Inspection Toolkit Checklist

Verify all items before departure:

Client Specification and BOM

Client approved sample (if applicable)

AQL sampling tables (Section 3 of this SOP)

Digital caliper (verify battery)

Tape measure (5 m)

3M test tape

Black/red permanent marker

Mobile phone, power bank

Handheld electronic scale