Examkin

Question

Difficulty: Very hardBolts, Nuts, and Washers

A mechanic removes a damaged hex bolt marked with exactly six radial lines on its head. The service manual specifies that a metric replacement of equivalent tensile strength can be used, provided it is secured with a castle nut and cotter pin. Which of the following correctly identifies the SAE grade of the original bolt, its equivalent metric property class, and the mechanical purpose of the specified nut combination?

  1. SAE Grade 8; Metric Class 10.9; provides a positive mechanical lock that prevents the nut from backing off under high vibration.Answer
  2. B
    SAE Grade 6; Metric Class 8.8; applies continuous spring tension to compensate for thermal expansion.
  3. C
    SAE Grade 8; Metric Class 12.9; cuts into the mating surface to create friction and resist rotational loosening.
  4. D
    SAE Grade 6; Metric Class 10.9; distributes the clamping load over a wider surface area to prevent damaging soft metals.

Answer

SAE Grade 8; Metric Class 10.9; provides a positive mechanical lock that prevents the nut from backing off under high vibration.
The correct combination accurately calculates the SAE grade by adding two to the six radial lines, correctly matches Grade 8 to its exact Metric Class 10.9 equivalent based on tensile strength, and correctly identifies that a castle nut paired with a cotter pin creates a physical barrier to prevent rotational loosening under severe vibration.

Step-by-Step Solution

1
Calculate the SAE bolt grade based on the head markings.
6 radial lines + 2 = SAE Grade 8.
The standard rule for identifying SAE fractional bolts is to add 2 to the number of radial lines on the bolt head to determine its grade.
2
Determine the equivalent metric property class for SAE Grade 8.
Metric Class 10.9.
An SAE Grade 8 bolt has a tensile strength of 150,000 psi. The closest equivalent in the metric system is Property Class 10.9, which has a tensile strength of 1040 MPa (approximately 150,800 psi).
3
Identify the mechanical function of a castle nut and cotter pin.
Provides a positive mechanical lock against vibration.
Unlike friction-based lock washers or spring-tension washers, a cotter pin passing through a drilled bolt shaft and the slots of a castle nut creates a physical barrier that makes it impossible for the nut to rotate, which is critical in high-vibration assemblies like steering linkages.

Key Concept

Fastener Grade Identification, Metric Equivalency, and Specialized Nuts
Rate this question

Topics

Bolts, Nuts, and Washers

More questions from this topic