Basic Tools: Combination Wrenches

There are several basic hand tools that everyone should own even if you don’t get into in depth projects like head gasket replacement.  At some point you’re going to need to adjust a bike seat, tighten a bolt on your fence gate, or use a real tool instead of that piece of crap that comes with assemble it yourself furniture.  One of the basic hand tools is the wrench and the most common is the Combination Wrench.   You can find them available in SAE and Metric sizes almost anywhere.  You’ll probably need a set of both.

Here’s an artsy picture of some Craftsman Pro’s I own.  Ooooh pretty chome!  They stopped making them in the US recently which is sad because they were great wrenches at a good price.  Better if you bought them on a great sale like I did!

The Combination Wrench gets is name due to the fact that it has a box end (green arrow) and an open end (red arrow).  The open end allows you to access a nut from the side and the box end allows you to access it from above.  There are a couple of ingenious bends in this wrench which enhance it’s usefulness.  The box end is rotated in the plane of the beam (blue arrow) at an angle of around 15 degrees so that the wrench can be flipped.  This is useful in tight spots where you can’t turn the fastener a full 60 degrees to get on another side of it.   The entire box end (black arrow) is also bent at an angle perpendicular to the beam which can help out in tight spots and will help avoid scraping you knuckles when you’re working on something on a flat surface.  The beam of the wrench (blue arrow) should not be overlooked.  If it has sharp edges on it you’ll be reminded of this when you have to push or pull on the wrench with any significant amount of force.

Combination wrenches come in a variety of shapes and sizes.  I’ll point out some of them in the picture below.  I’ll identify the wrenches by number starting from 1 at the top.  Differences in length is the most popular variation out there.  There are long pattern wrenches (1), regular length (4), and stubbies (11).  All have their use.  You also have an option of how many points in the box end.  Typically, you’ll have 12 points but sometimes you’ll have 6 points like in wrench (5).  12 point wrenches offer you twice as many ways to put the wrench on a fastener  and are what I’d recommend.  Some wrenches are supposed to fit pairs of metric and SAE sized fasteners such as (9) while others are twisted (10) so you’ll have a wider surface to press on.  Some wrenches have a box end that ratchets (12) and are a blessing in tight spots.  You probably won’t need ratcheting wrenches for mundane tasks but when working on a car they’re great.  Though I don’t have a picture of it here (I do own some), some wrenches have box ends that rotate between + and – 90 degrees allowing them to get into spots other wrenches and sockets can’t…such as a bell housing of a 99 Firebird.  Guess how I know??

Some wrenches such as Snap-On’s Flank Drive Plus and Wright’s SAE wrenches have teeth in the open end (yellow arrow).  They increase the torque than can be applied to a fastener by biting into the surface.  This can create indentions in the surface but sometimes it’s worth it.

Other wrenches, such as this FACOM, have a unique open end that concentrates all of the pressure on the flats of the fastener instead of the corners like regular open ends (more on flats vs corners and why it is importatn below).  I haven’t used this design that often but it looks like it should work very well.

In my limited experience the box end of the wrench is used a lot more than the open end of the wrench.  It is much stronger than the open end because of it’s design.  It won’t spread like an open end will.  Consequently,  there are some interesting design features here that aren’t as apparent as on the open ends.  The most basic design for a box end wrench has the wrench contacting the fastener on the corners (vertical edges).  This is bad because under high torque situations you’re likely to round the edges off of the fastener.  If the nut is rusty or deformed you’re also likely to do damage with this style of box end.   This style  is shown in the picture below.  You can see that the wrench contacts on the edges of the nut (red arrows).   Luckily, this style of box ends are only found on older wrenches, such as the 1960’s Craftsman (6), and super cheap wrenches, such as the Harbor Freight stubby (13).   You can pick this design out because the corners of the box end points are sharp (green arrow).  Luckily, there’s another design.

As I understand it, in the 1960s a company named Bonney patented a new design for the box end of a wrench that puts the pressure on the flats of a fasteners instead of the edge.  This results in much lower chance of rounding the fastener and the ability apply more torque to the stuck fastener.  Note in the picture below that the wrench is contacting the fastener on the flats (yellow arrows) and not the corners (red arrows).  The patent has long since expired and now this design is on most all wrenches out there.  It has been for a while so even if you find a used wrench it may still have this design.  You can pick this design out because the corners of the box end points are rounded.  There are variations on this design depending on what company you’re looking at.  They all have names for their designs but the idea is the same.  I’m sure there is an involved optimization problem to this style of box end with many good solutions.

To illustrate this corners vs flats thing,  I’ll present a couple pictures of some nuts.  In the next two pictures, the areas where the wrench contacts the nut is deformed and looks different than the smooth surface on the rest of the nut.  On the first picture the contact patch is right up against the edge.  The nut was torqued in both directions to show that the contacts patches are on the edge.  So, the contact patch in one direction would only be half as wide.  On the second picture the contact patch is moved away from the edge and is wider.

You can also show the same thing by putting dye on some nuts and then torquing them with a wrench.  Where the wrench contacts the dye is removed allowing the contact patch to be seen. In the first picture the contact point is again at the edge. On the second picture the contact point is on the flat and wider.

So, now that you know more than you ever wanted to know about combination wrenches, go forth and buy some.  Yes, you can have more than one, two, or three sets.  Tools, unlike laptop computers and pop stars on the radio, last for more than 2 years so go buy some good ones.  Also, store them in an organized fashion in a proper place so you can find them when the time comes.  On the other hand, if you’re going to throw them in the bottom of the closet or in a bucket of water may the tool gods have mercy on your soul!

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