Automotive Materials, Tools and Measuring Instruments
This domain tests materials selection and correct use of hand tools and measuring instruments. Expect questions on ferrous and non-ferrous metals, heat treatment, micrometers, vernier calipers, feeler gauges, dial indicators, and torque wrenches.
Core rules
- Ferrous metals contain iron: cast iron, mild steel, and alloy steel. Non-ferrous metals include aluminium, copper, brass, and magnesium.
- Heat treatment changes properties: hardening increases wear resistance, tempering reduces brittleness, annealing softens, and normalising refines grain structure.
- A vernier caliper commonly has a least count of 0.02 mm; a metric micrometer commonly reads to 0.01 mm.
- A torque wrench tightens fasteners to a specified value; it is not a breaker bar.
- A feeler gauge measures small gaps such as valve clearance; a dial indicator measures runout and end play.
Worked example
A metric micrometer has a 0.01 mm least count. The sleeve shows 5.5 mm and the thimble reads 23 divisions. Thimble value = 23 × 0.01 = 0.23 mm. Reading = 5.5 + 0.23 = 5.73 mm. The reasoning is to read the main scale first, then add the thimble fraction; check zero error before measuring and avoid over-tightening the thimble.
Traps that cost marks
- Using a torque wrench to loosen a seized bolt.
- Forgetting to check zero error on a micrometer or vernier.
- Reading a vernier at an angle, causing parallax error.
- Confusing hardening with tempering.
- Using a feeler gauge with oil or burrs on the blades.