Automotive Materials, Tools and Measuring Instruments
What this domain tests
Materials and their properties, hand and measuring tools, least count, calibration and correct tool use. Expect identification, property matching and simple instrument readings.
Core rules and concepts
- Ferrous materials contain iron: steel and cast iron. Non-ferrous: aluminium, copper, brass and bronze.
- Properties: strength resists load; hardness resists indentation; ductility allows drawing into wire; malleability allows hammering into sheet; toughness absorbs impact.
- Heat treatments: annealing softens and relieves stress; normalising refines grain; hardening increases hardness; tempering reduces brittleness after hardening.
- Aluminium is light and conducts heat well; cast iron is heavy, wear-resistant and damps vibration.
- Micrometer least count is usually 0.01 mm; vernier caliper 0.02 mm; dial gauge 0.01 mm; feeler gauge measures gaps; plastigauge checks bearing clearance.
- A torque wrench must be calibrated and used only to tighten, never to loosen.
Worked example
A vernier caliper has least count 0.02 mm. Main scale reads 12 mm and the 7th vernier division coincides. Reading = 12 + (7 × 0.02) = 12.14 mm. If the caliper has a positive zero error of 0.04 mm, actual size = 12.14 - 0.04 = 12.10 mm. Reason: always correct for zero error in the direction that removes the instrument's bias.
Traps that cost marks
Using an adjustable wrench on hex fasteners; reading a vernier with parallax; forgetting micrometer zero check; using a torque wrench as a breaker bar; mixing inch and metric readings.