What AQL is
Acceptable Quality Limit. It is a table, standardised, that says: for a batch of this size, inspect this many units, and if you find more than this many defects, reject the batch.
The number, 2.5 or 4.0, is the percentage of defective units the plan tolerates in the lot. Lower is stricter. It is not a description of your product. It is a description of how much risk you are accepting.
How defects get classified, and where the argument happens
Critical. A defect that makes the product unsafe or illegal. Zero tolerated, always.
Major. A defect a customer would notice and return the product for. The standard limit is 2.5.
Minor. A cosmetic imperfection a customer would probably accept. The standard limit is 4.0.
The classification is where the argument happens. Write your own defect list, with photographs, category by category, and attach it to the contract. Otherwise the factory's inspector will classify a scratch as minor and yours will classify it as major, and neither of you will be wrong.
How the numbers actually work
For a lot of 3,200 units at general inspection level II, the sample size is 125 units. At AQL 2.5 the accept number is 7 and the reject number is 8. Find seven major defects, the lot passes. Find eight, it fails.
That is the entire mechanism, and it is why the argument on the factory floor is always about the classification of the eighth defect. It is also why a defect list with photographs is worth more than any amount of goodwill.
What a report must contain
The lot size, the inspection level, the AQL used, the sample size, the accept and reject numbers, the defects found by classification, photographs of each defect, measurements against the specification, the packing and label check, and a recommendation to release or hold.
If it does not contain those, it is a photo album. And if the balance payment has already been made, even a perfect report is only a piece of paper: you have nothing left to hold.
- AQL is a sampling plan with a hard accept number, not a quality score.
- Critical zero, major 2.5, minor 4.0 is the usual starting point. Adjust by category.
- Write your own defect list with photographs and attach it to the contract.
- An inspection report is only leverage if the balance payment has not been made yet.
