Technical Japanese #10 — Quality Japanese: Defects, Inspection, Dimensions and Tolerances
No department in a Japanese plant demands tighter language than 品質 (hinshitsu). One misunderstanding about a tolerance or a limit sample can send a whole lot back. Quality vocabulary is judgement vocabulary: every term is attached to a pass-or-fail decision. This post collects the 品質 terms you meet most often at inspection (検査), and how they are used on the paperwork and in a defect report.
Core quality vocabulary
| Japanese | Reading | Meaning | Field note |
|---|
| 品質 | ひんしつ hinshitsu | quality | Name of the QC/QA department |
| 不良 / 不良品 | ふりょう furyō | defect, defective part | The opposite of 良品 |
| 良品 | りょうひん ryōhin | good part | A part that passes |
| 検査 | けんさ kensa | inspection | The main QC step |
| 合格 | ごうかく gōkaku | pass | Cleared inspection |
| 不合格 | ふごうかく fugōkaku | fail | Rejected |
| 寸法 | すんぽう sunpō | dimension | The measurement on the drawing |
| 公差 | こうさ kōsa | tolerance | The permitted plus-minus band |
| 限度見本 | げんどみほん gendo mihon | limit sample | The reference sample to compare against |
| 測定 | そくてい sokutei | measurement | With calipers, micrometer and so on |
| 規格 | きかく kikaku | standard, specification | JIS or an in-house standard |
| 規格外 | きかくがい kikakugai | out of specification | Beyond tolerance |
| 外観 | がいかん gaikan | appearance | Checked by eye |
| 異物 | いぶつ ibutsu | foreign matter | Contamination in the part |
| トレサビリティ | toresabiriti | traceability | Tracing a lot back through the process |
Tolerance (公差) and limit samples (限度見本) — the two easiest things to get wrong
- 公差 is the band allowed around the nominal dimension. 50 ±0.05 passes between 49.95 and 50.05 mm; outside it the part is 規格外 and therefore 不良. A one-sided tolerance, 20 +0.1 / 0, means 20.0 to 20.1 mm. Reading the sign or the direction wrongly is the most expensive mistake on this page.
- 限度見本 is a physical sample showing the boundary between pass and fail for defects that are hard to measure — scratches, colour, gloss. When you hear 限度見本と比べてください, fetch the reference sample and compare. Do not judge it by feel.
Two kinds of inspection — mixing them up means running the wrong process
| Japanese | Meaning | Used when |
|---|
| 全数検査 (zensū kensa) | 100% inspection | Safety-critical parts, or a small lot |
| 抜き取り検査 (nukitori kensa) | sampling inspection (AQL) | Large lots, lower cost |
| 官能検査 (kannō kensa) | sensory inspection | Properties hard to measure — use 限度見本 |
Ask before you start: この工程は全数検査ですか、抜き取りですか。 — Is this step 100% inspection or sampling?
Names for appearance defects (外観)
| Japanese | Reading | Meaning | Common cause |
|---|
| キズ / 傷 | きず kizu | scratch | Impact, clamping |
| へこみ | hekomi | dent | Knocks during transport |
| バリ | bari | burr | Worn tooling |
| 汚れ | よごれ yogore | dirt, stain | Poor cleaning |
| 変形 | へんけい henkei | deformation | Heat or force |
| 錆 | さび sabi | rust | Damp storage |
| 欠品 | けっぴん keppin | missing part | Assembly error |
| 混入 | こんにゅう konnyū | mixed-in wrong item | Lots mixed together |
Sentences from the inspection bench
- これは不良です。 — This one is defective.
- 寸法を測定してください。 — Please measure the dimension.
- 公差を超えています。 — It is outside tolerance.
- 限度見本と比べて、合格ですか。 — Compared with the limit sample, does it pass?
- 傷があります。外観不良です。 — There is a scratch. It is an appearance defect.
The safe structure for a defect report is object plus phenomenon plus judgement: "Part A — foreign matter — fail." Clear, and it does not assign blame. Always record the ロット番号 so the lot can be traced.
Mistakes to avoid
| Mistake | Why it hurts |
|---|
| Reading 50 ±0.05 as a single limit | It is a band, 49.95 to 50.05. Both the sign and the direction matter |
| Judging an appearance defect by eye | That is what the 限度見本 exists for — compare, do not estimate |
| Not asking whether the step is 全数 or 抜き取り | You end up running the wrong inspection process for the lot |
| Reporting 不良 without the lot number | Without ロット番号 the problem cannot be traced back through the process |
Read it, then act — quick self-check
- The drawing says 30 ±0.02 and you measure 30.03.
- You hear 限度見本と比べてください.
- The sheet says 全数検査.
- You see a scratch but cannot tell whether it is over the limit.
<details><summary>Answers</summary>
- 規格外, therefore 不合格 — 30.03 is above the 30.02 upper limit.
- Fetch the limit sample and compare; do not decide by eye.
- Inspect 100%, not a sample.
- Compare with the 限度見本. If still unsure, report it as 〜かもしれません rather than declaring 不良.
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Systematic defect analysis uses the QC7つ道具, the seven QC tools: 特性要因図 (fishbone), パレート図 (Pareto), ヒストグラム, 管理図 (control chart), チェックシート, 散布図 (scatter) and 層別 (stratification). When a colleague mentions パレート図 in an improvement meeting, they are prioritising the defect with the largest share.
Quick recall
- The judgement pairs: 良品 against 不良品, 合格 against 不合格, 規格内 against 規格外. Use them decisively.
- 公差 "50 ±0.05" means 49.95 to 50.05 — read the sign and the direction carefully.
- 限度見本 governs appearance defects; ask whether the step is 全数 or 抜き取り before you start.
- A defect report is object, phenomenon, judgement, and the ロット番号.
Do you have a lot that needs inspecting to Japanese standards, or a Japanese drawing or 仕様書 whose tolerances have to be broken down for machining? MINATA takes on reading Japanese drawings and specs, then designing and machining to Japanese 品質 standards. See MINATA's engineering services and projects we have delivered.
Next in the series: 生産技術 production engineering · drawing and tolerance vocabulary (図面・幾何公差・データム) · reading numbers and dimensions on a Japanese drawing.
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