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Difficulty: MediumWrenches

While servicing an imported compact vehicle, a technician must remove a stubborn 17 mm17\text{ mm} hex-head bellhousing bolt. Which tool should be used to safely loosen this fastener without rounding off its corners?

  1. A
    An 11/16 in11/16\text{ in} open-end wrench
  2. A 17 mm17\text{ mm} box-end wrenchAnswer
  3. C
    A 5/8 in5/8\text{ in} combination wrench
  4. D
    A 3/4 in3/4\text{ in} box-end wrench

Answer

A 17 mm17\text{ mm} box-end wrench
The 17 mm17\text{ mm} box-end wrench is specifically engineered for metric hardware of that dimension. Its enclosed ring contacts all six (or twelve) points of the hex head, providing maximum contact area and eliminating the slop that causes fastener damage.

Step-by-Step Solution

1
Identify the fastener measurement system and size
The fastener is metric with a nominal head dimension of 17 mm17\text{ mm} (17.00 mm≈0.669 in17.00\text{ mm} \approx 0.669\text{ in}).
Metric fasteners require dedicated metric tooling to ensure zero tolerance gap.
2
Evaluate the exact dimensions of fractional SAE alternatives
An 11/16 in11/16\text{ in} wrench equals 17.46 mm17.46\text{ mm}, 5/8 in5/8\text{ in} equals 15.88 mm15.88\text{ mm}, and 3/4 in3/4\text{ in} equals 19.05 mm19.05\text{ mm}.
Interchanging SAE fractional tools on metric fasteners introduces dimensional mismatches.
3
Select the correct tool size and profile for high-torque removal
The 17 mm17\text{ mm} box-end wrench provides exact sizing and continuous contact around all hex points.
Matching the metric size exactly prevents rounding corners, and a box-end design provides superior grip compared to an open-end wrench.

Key Concept

Metric vs. SAE Wrench Sizing and Fastener Fitment
Estimated Time:1m 0s
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Wrenches

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