The great utility of keys fixed size and open end as manual tools it has remained intact since the first prototypes appeared back in the fifteenth century. They were originally shaped like a socket wrench, and since there was no standard size, each wrench and fastener had to be individually built by a blacksmith.
However, it was since the Industrial Revolution, well into the 1700s, that the field of fixed keys open it expanded widely when, for example, the machines that would help the world produce more goods at lower cost were built and maintained. Very soon the wrought iron keys made by blacksmiths were replaced by versions of molten iron produced on a larger scale.
The standard sizes for fixed keys and fasteners (such as bolts, screws, bolts, nuts, etc.) were developed in 1825 to make these objects interchangeable between various pieces of machinery, that is, so that wrenches could be used on various fasteners, as well as various nuts on more than one bolt. This meant that any mechanic could work on a machine with his own keyset standardized instead of having a single set of keys for a given machine.
The need, however, to achieve high precision in order to improve production led to perfecting these standards, both for the heads of the fasteners and for the threads, and this is how, since the mid-nineteenth century, the Whitworth measures emerged in the United Kingdom, NPT in the United States, and metric in Europe, which we have already covered in this introduction and in this more detailed article.
Therefore, new fixed wrench sizes to accommodate the standardized measurements, both imperial and metric, of the ever-growing market for fasteners with various head sizes.
At the same time, the need was raised to further expand the adaptability of fixed wrenches when the clamping elements were in confined or hard-to-reach places in an engine, machine, frame or structure. That’s why the first ones appeared. curved keys like the ones we see below.
The rise of combination wrenches
And this would be just the beginning that brought about, already in the 20th century and with the advent of the automobile and motorcycle, the advent of a whole family of fixed keys designed to achieve the maximum possible adaptability and practicality.
That is why, back in the 1930s, the combined keys, a type of open-end wrench that, like socket wrenches, Allen wrenches, and socket wrenches or keyholes, serve a particular purpose. Combination wrenches typically feature one end open and one end in grooved ring, capable of perfectly adapting to the corresponding size nut or bolt head, as we see in these videos.
It is well known that after loosening a tight nut (or vice versa), it can be removed (or vice versa) much faster with an open end wrench than with a splined ring wrench. This means that a combination wrench is extremely useful in such a situation because there is no need to change tools as we can use the knurled end to loosen (or tighten) the nuts and then the open end for faster turning.
Some time ago we presented Of Machines and Tools a complete article on combination wrenches that describes the various designs that we can find on the market, both in individual versions and in sets of several keys that respond to the most common measures used in general.
If they are purchased as a set, manufacturers usually include a practical case that presents the keys perfectly arranged according to their size.
However. One question we could ask ourselves is what is the advantage of an open end wrench and/or a combination wrench. With the widespread use today of adjustable wrenches, such as the traditional crescent wrench, monkey wrench, Stillson wrench or socket wrench, which can handle a huge variety of fastener sizes on their own, you could It seems that the demand for fixed keys is in decline.
Nothing further from the truth. In plumbing jobs, for example, adjustable wrenches may be the usual tool. But the same does not happen in a car or motorcycle workshop.
What follows is what experts in the field have to say about their preference for open end wrenches over a conventional wrench, taking into account a number of parameters such as the following.
An adjustable wrench head is several times the size of an open end wrench. When working in tight spaces, very often there is only enough room to fit the smallest possible wrench around the bolt head.
b) Ease of use
Although a wrench can work with any bolt size within its adjustment range, if the job requires dealing with tens or even hundreds of the same bolts, it will become tedious having to constantly adjust the wrench to keep it at the correct size.
c) Rounding of the head/corners
This is perhaps the biggest advantage of fixed keys. If not adjusted correctly, a wrench will very quickly round off the corners of a hex bolt. So for fasteners that are in constant use, or in situations where gouging, breaking, or completely removing a bolt head would present a serious problem, a fixed wrench This will ensure that the bolt has a long service life. In aeronautics, for example, adjustable wrenches are generally prohibited due to their tendency to round off the nuts.
Wrenches can wear out, while open-end wrenches never really wear out, unless of course they are abused, and for much longer than an adjustable wrench.
It is extremely difficult to get good torque with a wrench. Instead, when using the knurled ring of a combination wrench, not only can you be sure you have the right size that fits the nut perfectly, but it can also be tightened securely.
A quality wrench is much more expensive than a fixed size wrench. When we realize that we’d need to cut the handle of our wrench to fit into a tight space, or that we’d need to bend it into an odd shape to fit around a pipe, we’ll appreciate having a combination wrench on hand that’s just the right size to fit. the job, not a shiny adjustable wrench that cost us 10 times as much.
This is an incomparable advantage in which, given its importance, we are going to dwell a little more.
The vast majority of combination wrenches have the design that we have seen in the videos at the beginning of this article. That is, the top view and the side view of the tool show, respectively, the design represented in this figure.
In other words, open end jaws angle 15 degrees with respect to the main axis of the tool, while knurled end offset 15 degrees with respect to the horizontal plane of the tool, forming an elbow.
East double angled and elbowed design responds to the norm DIN 3113 and it is what gives the combination wrench the advantage that no adjustable wrench can match.
Why? Let’s analyze each case.
a) What is the open end with an angle of 15 degrees for?
Let us observe the series of situations shown in the following scheme.
In other words, the 15 degree angle of the open end ensures sufficient turning arc in confined spaces so that, just by turning the key, it can always position itself or fit on two parallel faces of the nut and thus be able to turn it easily.
b) What is the knurled ring bent at an angle of 15 degrees for?
Again, let’s think about confined spaces and/or hard-to-reach objects, as this image shows.
It is worth saying that if we must work with aligned bolts between which turning a flat wrench would be impossible, or if we have one or more bolts inside a confined space, the elbow that forms the handle of the tool at its closed end will allow us an adjustment. or perfect loosening, a situation that a wrench, for example, could not overcome.
This explains the practicality of the design of combination wrenches that responds to the DIN 3113 standard and whose advantages compared to the DIN 3110 flat design can be compared in the following two figures.
In other words, while a flat combination wrench (DIN 3110) will have torque limitations depending on how easy it is to access the fastener, a wrench with an offset end (DIN 3113) can work perfectly and without limitations thanks to its two DIN versions. 3113 A (slight undercut) and DIN 3113 B (deep undercut) that accommodate not only tight spaces, but the situation where the fasteners themselves can get in the way of each other to achieve the correct grip and torque.
To visualize it better, a practical and very simple application of a combination wrench One of these features (or even a wrench with both ends closed) that cannot be done with any adjustable wrench is the one shown in this image.
As we can see, the most appropriate way to access this nut that secures the wheel of a tool trolley (or at that time any other type of movable furniture) is undoubtedly with an offset wrench.
Of course, as a final note, it should be clarified that if we carry out work at height, at risk of contact with electricity, or in sterile or corrosive environments, we can also have combination wrenches according to these needs. Some manufacturers offer their combination wrench sets with anti-fall, insulating properties, and even built in stainless steel, which will ensure excellent performance, with all the advantages mentioned here, where they are required.