Does AQL 2.5 mean the defect rate stays under 2.5 percent?

Answer: No. It is an acceptance limit across a supply history, and one lot may still release five defectives; a lot running 5 percent bad passes 79 percent of the time.

Why is the sample so different at 500 and at 520 pieces?

Answer: The table steps by band. 281 to 500 draws 50 pieces, 501 to 1200 draws 80, so 20 more cases buy 30 more samples. Set the band by delivered quantity.

Is full inspection safer than sampling?

Answer: Only slightly. After four hours the miss rate reaches 3 percent, so 800 pieces may release 12 or more, at 9.3 times the cost. Keep it for expensive custom work and first batches.

What must the inspection report contain?

Answer: Batch and sample size, defect class, verdict, measured values, photo numbers and a dated signature. Drop the sample size and nobody can recompute the result.

Can a re-inspection be made stricter?

Answer: Yes, if it is agreed first. Doubling to 160 pieces at Ac 10 / Re 11 is the normal step; returning the batch after two failures on one item is the strictest.

Protective Case Inspection: AQL 2.5 vs 100%

Quick answer: AQL 2.5 turns a batch of 800 into 80 sampled pieces with Ac 5 / Re 6, at 0.12 USD per case, while checking all 800 costs 1.12 USD each.

Batch Size First, Then the Sampling Number
AQL 2.5 in Practice: 80 Pieces from 501 to 1200
Six Checks and Their Limits
Cost of 100% Inspection and Three Cases For It
Six Columns of the Inspection Report
Re-inspection and Disputes
FAQ

1. Batch Size First, Then the Sampling Number

The same plan reads differently at 480 pieces and at 520: one lands on 50 samples, the other on 80. Forty extra cases buy 30 extra samples, and minutes per case climb from 0.104 to 0.154.

So the first line is not an AQL value but the batch band, fixed at general inspection level II. Cross a band and the sample steps up, which moves both the price and the delivery date.

Batch (pieces)	Sample (pieces)	Ac	Re	Minutes per case
151–280	32	2	3	2.4
281–500	50	3	4	1.5
501–1200	80	5	6	0.9
1201–3200	125	7	8	0.6

The usual loophole: a supplier quotes a 500-piece lot and ships 620, keeping the sample at 50 and Ac 3 / Re 4, which lowers the bar.

2. AQL 2.5 in Practice: 80 Pieces from 501 to 1200

In the 501 to 1200 band, AQL 2.5 means 80 samples with Ac 5 / Re 6: five defectives or fewer pass the batch, six reject it.

AQL 2.5 sampling run on a blue case head on, lid closed, folding handle in a top notch, two feet below

The 2.5 is not a ceiling on one batch but the acceptance limit across a supply history. A lot running 2 percent bad draws six or more from 80 pieces about 0.6 percent of the time, so 99.4 percent pass. At 5 percent bad the figure is 21 percent, meaning 79 percent still get through.

Tightening a single batch means a stricter level or a lower value, for example AQL 1.5, which lands on Ac 3 / Re 4 in the same band.

3. Six Checks and Their Limits

Whether the plan carries limits decides whether a dispute has anything to stand on. Only the drop test destroys samples.

Check	Method	Limit	Samples
Appearance	Visual, 600 mm, 1,000 lx, 10 s	No deep score, colour ΔE ≤1.5	80
Dimensions	Calipers at three points	±2 mm on length, width, height	5
Latch force	Push-pull gauge, straight closure	180 N to 260 N	5
Seal	0.3 mm feeler around the rim	Feeler does not enter	5
Air tightness	0.3 bar held for 60 s	Drop ≤0.05 bar	5
Drop	1.2 m, six faces, three edges, one corner	No crack, latch stays shut	3

Appearance starts most arguments: with no gauge for scratch depth, use three numbered limit plates and judge against the plate.

Latch force is a window, not a floor: below 180 N the lid will not seat, above 260 N one hand cannot close it.

4. Cost of 100% Inspection and Three Cases For It

For 800 cases, full inspection at 2.1 minutes each is 28 hours, or 896 USD, which is 1.12 USD per case. Sampling 80 pieces plus five airtightness tests takes 3.1 hours and 99 USD, or 0.12 USD per case, a 9.3 times gap.

AQL 2.5 full inspection of a bright yellow case, lid shut, arched handle centred over a notch, one foot under the base

Item	80 samples	All 800
Inspection hours	3.1 h	28 h
Labour	99 USD	896 USD
Cost per case	0.12 USD	1.12 USD
Destructive drops	3 pieces	6 pieces

Full inspection is not zero-escape either: after four hours the visual miss rate rises to 3 percent, so 800 pieces may release 12 to 24 defectives, while sampling lets at most five through.

Those cases: custom cases above 200 USD, models with a complaint rate above 1.5 percent, and the first 200 pieces of a new tool.

5. Six Columns of the Inspection Report

A report without the sample size cannot be recomputed, and a result that cannot be recomputed cannot be reviewed. Six columns: batch and sample size, defect class, verdict, raw readings, photo numbers, signature and date.

Class defects as critical, major or minor. Critical means the protective function fails, such as an airtightness drop above 0.05 bar, where one piece rejects the batch. Each class runs its own Ac / Re, never pooled.

Raw readings are recorded as measured: 212 N, 228 N, 196 N beats three ticks. Photo numbers must match report numbers, one shot each for case, defect and gauge reading, and two signatures close the report.

6. Re-inspection and Disputes

Fix the rule before the first rejection. The common form doubles the sample to 160 at Ac 10 / Re 11, covering the failed item plus appearance, never a second drop test.

Two consecutive rejections on one check return the batch, with no third attempt.

Disputes go back to retained samples: 3 pieces sealed for 90 days, whose score, colour and latch force are the reference; the responsible side pays.

Conclusion

The cost gap in an inspection plan comes from the sample size and the batch band, not from inspector speed. Four checks settle it: whether the sample follows the batch band; whether Ac and Re run per defect class; whether full inspection is reserved for cases above 200 USD, models above a 1.5 percent complaint rate and the first 200 pieces; and whether re-inspection steps, retention and cost allocation sit in the contract. Get all four right and the plan blocks defects without paying for checks nobody needs.