During a routine alternator replacement, an automotive technician must tighten a hex-head … — Armed Services Vocational Aptitude Battery (ASVAB)

During a routine alternator replacement, an automotive technician must tighten a hex-head mounting bolt that measures $15\text{ mm}$ across the flats. The technician cannot locate the $15\text{ mm}$ wrench and considers substituting a standard fractional $5/8\text{ in}$ wrench from an SAE tool set. Which of the following describes the most likely outcome of using this fractional wrench?

A
The wrench opening will be significantly undersized at approximately $14.29\text{ mm}$ , preventing it from slipping over the bolt head.
The wrench opening will be oversized at approximately $15.88\text{ mm}$ , causing a loose fit that can slip and round off the bolt corners.Cevap
C
The wrench will provide an exact dimensional match because $5/8\text{ in}$ converts precisely to $15.00\text{ mm}$ in standard automotive fastener sizing.
D
The wrench will bind against the fastener corners with severe interference, causing the box-end opening to crack or stretch.

Cevap

The wrench opening will be oversized at approximately

15.88\text{ mm}

, causing a loose fit that can slip and round off the bolt corners.

Converting

5/8\text{ in}

to metric yields

0.625 \times 25.4 = 15.875\text{ mm}

. Because

15.875\text{ mm}

is noticeably larger than the

15\text{ mm}

bolt head, the wrench fits loosely with

0.875\text{ mm}

of play. Applying tightening torque with this loose fit causes the wrench jaws to ride over the fastener vertices, rounding off the hex head.

Adım Adım Çözüm

Convert the fractional SAE wrench size (

5/8\text{ in}

) to decimal inches.

5 \div 8 = 0.625\text{ in}

Converting to decimal form simplifies conversion to metric units.

Convert decimal inches to millimeters using the standard conversion factor (

1\text{ in} = 25.4\text{ mm}

0.625\text{ in} \times 25.4\text{ mm/in} = 15.875\text{ mm}

Determining the metric equivalent allows direct comparison to the

15\text{ mm}

fastener head.

Calculate the clearance gap between the wrench jaw opening and the fastener head.

15.875\text{ mm} - 15.000\text{ mm} = 0.875\text{ mm}

(approximately

0.034\text{ in}

)

Clearance determines whether the tool makes solid flat contact or slips onto the corners.

Evaluate the mechanical consequences of excessive clearance under torque.

The oversized wrench contacts only the extreme tips of the hex vertices rather than the flats, causing slippage and corner rounding.

Proper torque transfer requires tight engagement across fastener flats.

Anahtar Kavram

Metric and SAE Wrench Incompatibility and Fastener Corner Rounding

Alternatif Yöntem

Memorizing key baseline equivalents (

1/2\text{ in} \approx 12.7\text{ mm}

9/16\text{ in} \approx 14.3\text{ mm}

5/8\text{ in} \approx 15.9\text{ mm}

) allows rapid estimation of SAE-to-metric clearances without manual division.

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