Automotive Materials, Fasteners and Measurement
What the exam tests
Questions cover ferrous and non-ferrous metals, plastics, material properties, bolt grades, thread types, washers, locking methods and precision measuring tools.
Core rules
- Steel and cast iron are ferrous; aluminium, copper and brass are non-ferrous. Aluminium is light but corrodes differently from steel.
- Properties include strength, hardness, ductility, brittleness and fatigue resistance. A bolt grade marking shows tensile strength class, not spanner size.
- Use the correct thread pitch and length. Torque values assume clean, lubricated or dry threads as specified; do not guess.
- Vernier caliper least count is commonly 0.02 mm; micrometer least count is commonly 0.01 mm. Check zero error and avoid parallax.
Worked example
A vernier caliper has a main-scale reading of 12 mm and the 24th vernier line aligns. With least count 0.02 mm, vernier reading = 24 × 0.02 = 0.48 mm. Total = 12.48 mm. Reasoning: read the main scale before the zero of the vernier, then add the aligned vernier fraction. Estimating the aligned line by eye causes error.
Traps that cost marks
Mixing millimetres and inches, ignoring zero error, over-tightening a bolt to compensate for a wrong grade, and using an adjustable wrench on precision hex fasteners.