A technician is securing an 11\text{ mm} hex-head bolt on an engine bracket and considers … — Armed Services Vocational Aptitude Battery (ASVAB)

A technician is securing an $11\text{ mm}$ hex-head bolt on an engine bracket and considers using a standard fractional $7/16\text{ in}$ wrench. Why is substituting this fractional wrench for the metric fastener improper?

A
The $7/16\text{ in}$ wrench is slightly smaller (approximately $10.85\text{ mm}$ ), preventing the tool jaws from seating fully over the bolt head.
The $7/16\text{ in}$ wrench is slightly larger (approximately $11.11\text{ mm}$ ), creating loose clearance that can round off the fastener corners under torque.Answer
C
The $7/16\text{ in}$ wrench alters the bolt's metric thread pitch during tightening, leading to stripped internal threads.
D
The $7/16\text{ in}$ wrench provides improper mechanical leverage because fractional wrenches only turn fasteners clockwise.

Answer

Substituting a

7/16\text{ in}

wrench for an

11\text{ mm}

fastener is improper because

7/16\text{ in}

equals approximately

11.11\text{ mm}

; this oversized fit creates excess clearance that slips and rounds off the bolt head corners under applied torque.

Using a standard fractional

7/16\text{ in}

wrench on an

11\text{ mm}

fastener introduces improper clearance because

7/16\text{ in}

converts to

11.1125\text{ mm}

(

0.4375\text{ in} \times 25.4\text{ mm/in}

). Because the tool opening is larger than the

11.00\text{ mm}

bolt head, the wrench cannot make full, flat surface contact with the hexagonal flats. When torque is applied, the wrench slips and concentrates force onto the points, rounding off the fastener corners.

Step-by-Step Solution

Convert the fractional SAE wrench size (

7/16\text{ in}

) to millimeters.

7/16\text{ in} = 0.4375\text{ in} \times 25.4\text{ mm/in} = 11.1125\text{ mm}

Converting both dimensions to the same unit allows direct comparison of tool opening and fastener width.

Compare the wrench opening (

11.11\text{ mm}

) to the target fastener head (

11.00\text{ mm}

) and evaluate the mechanical impact.

The wrench opening is

0.11\text{ mm}

larger than the fastener head.

Excessive clearance between the wrench flats and the fastener forces torque onto the sharp points/corners of the hex head, leading to rounding and tool slippage.

Key Concept

Wrench Sizing and Metric vs. SAE Fastener Compatibility

Estimated Time:1m 0s

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