Seibishi 3kyu › Measuring tools
Measuring tools in the Class 3 exam: reading them and common mistakes
Measuring tool items appear in all three Class 3 subjects. They ask which tool measures what, how to read it and which handling is wrong. This page sums up the tools you will meet.
Last updated: 2026-10-19
Tools you will meet
| Tool | Used for | Note |
|---|---|---|
| ノギス (vernier caliper) | Outside and inside diameters, depth | Light, even pressure; read straight on |
| マイクロメータ (micrometer) | Outside diameter to 0.01 mm | Use the ratchet stop (ラチェット) for even force |
| ダイヤル・ゲージ (dial gauge) | Runout, bend, end play | Plunger square to the surface |
| シリンダ・ゲージ (bore gauge) | Cylinder bore, wear, taper | Zero it with a micrometer first |
| シックネス・ゲージ (feeler gauge) | Valve clearance, plug gap, ring end gap | A slight drag means the right size |
| プラスチ・ゲージ (Plastigage) | Oil clearance of crank and rod bearings | Do not turn the shaft while it is clamped |
| トルク・レンチ (torque wrench) | Tightening to a specified torque | Not for loosening bolts |
| サーキット・テスタ (circuit tester) | Voltage, current, resistance, continuity | Current: series; voltage: parallel |
| 比重計 (hydrometer) | Battery electrolyte specific gravity | Correct for temperature |
Reading a micrometer: example
The sleeve shows the 7 mm line plus one half-millimetre line: 7.5 mm. On the thimble, line 23 meets the reference line: 0.23 mm. Result: 7.5 + 0.23 = 7.73 mm. A common mistake is missing the 0.5 mm line on the lower half of the sleeve.
Reading a vernier caliper: example
The vernier zero sits just past the 24 mm line on the main scale. The 7th vernier line (0.05 mm type) lines up with a main-scale line: 7 × 0.05 = 0.35 mm. Result: 24 + 0.35 = 24.35 mm.
The circuit tester in items
Items often show a circuit diagram and ask where to put the probes. Remember three rules: voltage in parallel, current in series, resistance with the circuit unpowered. For large currents such as starter current, use a clamp meter.
Practise in the app
Every subject in the app has measuring tool items with redrawn figures and step-by-step reading explanations. The Japanese tool names are in the parts names table.
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Sources checked on 2026-10-19: the JASPA registration test page and its 2026 (令和8) guide, the JASPA results for the 2025 first session, the JASPA past papers page and the MLIT press release on the new mechanic qualifications. Rules can change, so check the latest version at these sources.
FAQ
How fine does a vernier caliper read?
Workshop calipers usually read to 0.05 mm or 0.02 mm depending on the vernier scale. The item will show a figure or give the vernier division.
How do I read a micrometer?
Read the sleeve (each line 0.5 mm), then add the thimble line (each 0.01 mm) that meets the reference line.
How is a circuit tester connected to measure current?
In series with the circuit. Voltage is measured in parallel. Resistance is measured with the circuit's power off.
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