Single Sampling Plan Picker
Single sampling from MIL-STD-105E (1989) [1]; its double and multiple plans (Tables III and IV) are not on this page. The civilian successor is ANSI/ASQ Z1.4: check its current edition rather than assuming its tables match these.
Level II is the usual choice; I discriminates less, III more. S-1 to S-4 keep samples small where large sampling risks are acceptable, so pick an AQL that suits them (4.9.1).
Switching Rules
| Switch | When (in short), clause |
|---|---|
| Start → Normal | Every product starts on normal inspection. Each class of defects or defectives switches on its own. (4.6) |
| Normal → Tightened | 2 of 2, 3, 4 or 5 consecutive lots rejected on original inspection (resubmitted lots not counted). (4.7.1) |
| Tightened → Normal | 5 consecutive lots accepted on original inspection. (4.7.2) |
| Normal → Reduced | All of: the last 10 lots (or more, per Table VIII) on normal inspection and all accepted on original inspection; their samples’ total defectives (or defects) within the Table VIII limit number; steady production; reduced inspection judged desirable. (4.7.3) |
| Reduced → Normal | Any of: a lot rejected; a lot accepted with more than Ac but fewer than Re found; production irregular or delayed; other conditions call for it. (4.7.4, 4.10.1.4) |
| Tightened → Stop | 5 lots in all not accepted in a run of consecutive lots on original tightened inspection: stop accepting under the standard until the cause is corrected, then resume on tightened. (4.8) |
Paraphrased from MIL-STD-105E [1]. Table VIII (limit numbers for reduced inspection) is not on this page.
Table I — Sample Size Code Letters
Code letter by lot or batch size and inspection level, MIL-STD-105E [1].
Table II-A — Single Sampling, Normal Inspection
Ac/Re: accept the lot with Ac or fewer defectives (or defects) in the sample, reject it with Re or more. ↓ use the first plan below the arrow, ↑ the first plan above it, with that row’s sample size; where the sample size equals or exceeds the lot size, inspect 100 %.
Table II-B — Single Sampling, Tightened Inspection
Arrows and Ac/Re as in Table II-A. Code letter S (3150) is not in Table I; only the arrows of the 0.025 column lead to it.
Table II-C — Single Sampling, Reduced Inspection
Arrows as in Table II-A. Where more than Ac but fewer than Re are found, accept the lot but return to normal inspection from the next lot (4.10.1.4). Code letters A, B and C all take a sample of 2.