Tool time: Test your knowledge on wrenches

Richard Wright
Tags: workplace safety

Take this 14-question exam on wrenches and see how you do. You may be surprised by the results.




  1. If you borrow your buddy’s wrench and it breaks is this proof that you did something wrong?

    Answer:      No.  The wrench may already have had a small crack as a result of being overloaded in the past.  It is possible the wrench was badly worn or deformed from heavy use.  Wrenches that are badly worn are weaker than new wrenches.  It is always a good idea to carefully inspect a wrench before using it — even your own.

  2. What is the difference between a shear bolt and a tension bolt?  Why is this important?

    Answer:  A tension bolt is a bolt that is loaded in such a way that it tends to stretch the fastener.  A shear bolt is loaded with the load crosswise to the fastener.  A shear bolt needs to only be tightened enough so it does not work loose, or it may be secured with a cotter pin.  A tension bolt must be tightened to the correct amount, neither too much nor too little, or it is liable to break.  Some joints have a combination of crosswise and lengthwise loading.  These should always be considered tension bolts and carefully tightened. 

  3. Is it better to over-tighten or under-tighten a bolted joint?

    Answer:  Both over-tightening and under-tightening of bolts is bad.  Most bolts have additional load put on them after they have been put in use.  If they have been over-tightened, this additional load may cause the bolt to break.  If it has been under-tightened, the addition of a varying load may be enough to cause a slight gap in the joint assembly.  At this point in time, there is no load on the bolt.  The tension oscillates from no load to a substantially higher than the tightening load.  This high percentage of cyclic loading can cause a “fatigue” failure after a number of cycles, which can be as few as two or three or as much as a million.  The answer to the question is that bolts should be tightened to the specified tension or torque, no more and no less.

  4. If I can’t turn a bolt by hand would it be better to use a cheater bar, a slugging wrench, or an impact gun?

    Answer:  An impact gun is the safest and best way of removing a very tight bolt.  Not only is it much safer than a cheater bar, but the pulses produced by an impact gun are more effective than a steady pull.  If an impact gun or power to run a gun is not available, a slugging wrench is a good choice.  They are particularly useful for large fasteners.  

  5. When do you need to know the grade of a fastener?
    Answer:  There is no need to know the grade of a fastener to remove it.  If you need to replace it, you should replace it with a fastener of the same or higher grade.  If you are installing it, it is best to have an engineered recommendation.  If that is not available, you can look into a handbook for a recommendation.  To do this, you need to know the grade of the bolt to avoid either under-tightening or over-tightening. 

  6. Is a worn wrench as strong as a new wrench?

    Answer:  A worn wrench is never as strong as a new wrench.  A worn wrench on a worn fastener is even more likely to break.  Also, a worn wrench is more likely to damage the corners of a fastener.  When this happens, it may not be possible to remove the fastener with a brand new wrench.

  7. What fasteners should never be reused?

    Answer:  Fasteners in high strength applications should never be reused even if they look to be in good shape.  Fasteners not only get worn but accumulate internal microscopic damage as a result of cyclic fatigue.  Therefore, fasteners used in transportation which could cause loss of life in their failure should never be reused. 

  8. What problems do 12-point fasteners present?

    Answer:  Most 12-point fasteners are used in aerospace where it is always important that the fastener not fail.  Twelve-point fasteners are always designed to have smaller heads than normal which means they require a higher load on the wrench than a six-point fastener would impose on a wrench.  At the same time, they are higher strength at least 180,000 psi and sometimes higher.  This requires the best rate of wrenches in good condition.  Wright Tool makes spline wrenches which have been designed to turn both 12-point or 12 spline fasteners. 

  9. Does it make any difference what sequence you tighten lug bolts in Canada?

    Answer:  Yes.  If you do it the wrong way, you are in violation of the law.  For any joint with multiple fasteners, it is important that the fasteners be equally tight which can occur only if tightened in the proper pattern because increasing the load on one fastener can reduce the load on another fastener.  If the fasteners are unequally loaded, the fastener with the extra load may fail putting an additional load on the remaining fasteners.  Then the most heavily loaded of the remaining fasteners will break putting higher load on the remaining fasteners, and so forth until they are all broken or disaster occurs first.

  10. Why don’t fastener manufacturers put a suggested torque value on their packaging?

    Answer:  The correct torque or fastener depends on factors beyond the manufacturer’s control.  Is it going to be used on a shear joint or a tension joint?  Are the threads it engages with well formed? Is the joint lubricated at the time of assembly?  If a torque wrench is used, is the torque wrench in calibration?

  11. Why don’t wrench manufacturers put a suggested maximum torque for their wrenches?

    Answer:  The maximum torque that a wrench will transmit to a fastener without breakage or damage to the fastener depends not only on the wrench but also on the fastener’s wrenching areas.  Are they under size or rounded or rusty, oiled or dry?

  12. Is penetrating oil worth using?

    Answer:  Penetrating oil is always a help in loosening fasteners.  There are some situations where oil is not permitted. 

  13. What’s the best wrench for a tubing fitting?

    Answer:  An open end type of wrench is normally required.  There are special open end wrenches with a narrow gap so as to make contact with six sides of the fastener.  These reduce the chance of squeezing a fastener which may cause leakage.  Ordinary open end wrenches should not be used because they make contact on two corners and tend to deform the fastener.  However, special designs of open end wrenches such as WRIGHTGrip® contact at four points on the fastener and do it in a controlled fashion that reduces damage to the fastener yet allows higher torque. 

  14. Is a box wrench or an open-end wrench fastener stronger?

    Answer:  On combination wrenches, the open end is usually about a third of the strength of the box end, and, therefore, should not be used for high torque.  Not only can the wrench break, but the fastener is more likely to be damaged.  The WRIGHTGrip open-end wrench has a patented profile that applies force to the fastener in a very controlled manner, is as strong as a box wrench, and does less damage than a conventional open-end wrench.

About the author:
Richard Wright is the chairman of Wright Tool, a manufacturer of hand tools. For more information, visit

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