A mechanic needs to break loose a stubborn, corroded hydraulic brake line fitting with a n… — Armed Services Vocational Aptitude Battery (ASVAB)

A mechanic needs to break loose a stubborn, corroded hydraulic brake line fitting with a nominal hexagonal size of $11\text{ mm}$ without rounding off the fastener or damaging the tubing. Which of the following wrench types and sizes is the most appropriate to use?

A
A $7/16\text{ in}$ open-end wrench
B
An $11\text{ mm}$ open-end wrench
An $11\text{ mm}$ flare-nut wrenchAnswer
D
A $7/16\text{ in}$ flare-nut wrench

Answer

11\text{ mm}

flare-nut wrench

The

11\text{ mm}

flare-nut wrench is the correct choice because hydraulic line fittings are made of relatively soft alloys and are attached to fixed tubing. A flare-nut wrench wraps around five of the six hexagonal flats to maximize contact area and prevent jaw spread, while the precise

11\text{ mm}

dimension eliminates the loose clearance that causes fastener rounding.

Step-by-Step Solution

Determine the necessary tool geometry for hydraulic tubing fittings.

A flare-nut (line) wrench is required because it features an open slot to slide over the fluid pipe while enclosing five flats of the hexagonal fitting to distribute torque evenly.

Standard box-end wrenches cannot slide over fixed tubing, and open-end wrenches only grip two flats, easily spreading and rounding softer line nuts.

Evaluate the sizing tolerance between metric and fractional SAE dimensions.

11\text{ mm} = 0.4331\text{ in}

, whereas

7/16\text{ in} = 0.4375\text{ in} = 11.1125\text{ mm}

Using a

7/16\text{ in}

wrench on an

11\text{ mm}

fastener introduces over

0.11\text{ mm}

of loose clearance, causing the wrench jaws to slip over corners when applying high breakaway torque.

Combine the optimal tool design with the exact nominal size.

Select the

11\text{ mm}

flare-nut wrench.

This guarantees exact fitment and maximum contact surface without rounding the corroded fitting.

Key Concept

Selection of specialized flare-nut wrenches for tubing fittings and adherence to exact metric versus SAE sizing tolerances.

Estimated Time:1m 15s

Question

Answer

Step-by-Step Solution

Key Concept

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