Look inside the average enthusiast tool box and you’ll find they all have something in common—box end and combination wrenches.

They’re the backbone of a good tool collection, because the basic box end wrench (or the box end part of a combination wrench) is the perfect tool for tightening and loosening nuts and bolts. Compared to an open end wrench, the box end wrench is obviously engineered to grasp the nut or head of the bolt on all sides. That way, there’s little or no chance for the wrench to slip. It also means you apply more force to the wrench to loosen or tighten a given fastener.

The basics for a box end are simple: The opening for the nut or bolt head in a box end wrench differs from that of the open end wrench in that its closed. Due to the closed opening, it’s necessary to slip the end of the wrench over the nut or the head of the bolt. In contrast, an open end wrench can slide from the side (at least in most instances).

The machined edges (AKA “points”) that surround the interior of the opening in a box end grip the bolthead or nut securely. But they’re not 100 percent tight. Typically, the opening in the head of the wrench is 0.005 to 0.150 inch larger than the size stamped or engraved on the wrench. This is what allows it to slip over the nut or bolt with little effort. And different manufacturers have different takes on the design of the points. Keep in mind the size of the wrench actually refers to the distance across the flats of the nut or the head of a bolt it is designed to tighten or loosen.

You’ll often find that wrenches of smaller sizes (with smaller openings) are shorter in length than wrenches with large openings. This isn’t cast in stone however. There are definitely some exceptions and we’ll get into that further down this article. Tool manufacturers will tell you that the length of the wrench versus the wrench size is established so that you can apply a reasonable amount of torque to the fastener. Basically, they don’t want to be responsible for shearing off fasteners from excessive torque.

On a similar note, it’s not really a good idea to apply additional leverage on the wrench by using a piece of pipe as an extension. It’s also not good idea to use a hammer on the end of a wrench to loosen a fastener.

But most of us do both of these “wrongs” anyway!

The reason tool companies warn you to refrain from these practices is because it can crack, bend, or break wrenches. The additional leverage can also round corners on nuts or bolts, excessively stretch the fastener or break it outright (there are wrenches designed specifically to be struck, but that’s another story).  

The box end wrench is offered in either six point opening or a 12 point configurations, with the 12 point being the most common by far. The 12 point is perfect for general use along with work in cramped quarters. Here, the configuration allows the fastener to be turned though an arc of only 15 degrees through half a turn before it is necessary to reposition the wrench for another swing. The 12 points of a box end wrench exert pressure on the six points of a nut or bolt head instead of just two points when compared to an open end wrench. For stubborn jobs or on damaged nuts or boltheads though, the six point box end wrench is the best choice (but again, these tools aren’t as common as 12 point examples). The six point wrench grips the nut or bolthead across each flat, thereby reducing slippage to a bare minimum.

The offset of the wrench refers to the angle between the head of the wrench and its handle. The purpose of offset wrenches is to gain greater access to recessed bolts or nuts and to provide greater hand clearance. Single offset means a single bend or angle exists between the head of the wrench and its handle. On the other hand, a double offset means a wrench has two bends or angles between its head and handle. The standard angle of the single offset wrench is approximately 10 degrees while the double offset angles are approximately 45 degrees,

Everything that applies to box end wrenches applies to combination wrenches. Obviously, this is a convenient type of wrench to have in your collection. It has the speed of the open end wrench for running down a nut or bolt and the strength of a box-end wrench for completely tightening a nut or bolt.

Open end wrenches typically perform the best when placed squarely on the nut or the head of the bolt and pulled toward you. If you look at an open end wrench, you’ll see there’s a long and a short side at the opening. In order to exert less strain on the nut or bolt, try to make it a practice to place the wrench (on the fastener) so that the long side of the opening moves in the direction of the force being applied. In addition, by pulling the wrench instead of pushing on the it you can usually avoid skinning your knuckles if the wrench slips.

For the sake of convenience, box end and combination wrenches are available in different lengths. These different lengths are sometimes referred to as dwarf (or stubby), midget, standard or extra-long. The idea behind the different specialty lengths is to allow you to gain access to those hard-to-reach fasteners. An example is where you have little room for a wrench and even less room for wrench swing. That’s where the stubby comes into play. Obviously if you’re using an extra-long box end or combination wrench, take some care when the fastener. Given the extra handle length, it’s not difficult to overtighten the bolt or nut.

We took a closer look at the pros and cons of different length sockets and wrenches here.

One other specialized box end wrench is the “angle head”. This is a special purpose wrench made specifically for removing hard-to-get-at fasteners. The most common angle head you’ll find is used to access distributor hold down bolts. Often, angle heads are built for specific jobs for specific makes, models and years of automobiles.

As you can see, there’s a bit more to the common box end or combination wrench than first meets the eye. In the photos that follow, we’ll show you several different examples from the Summit Racing catalog along with examples from the writer’s tool box. Some of these are shiny and near new. Others are ancient and battle scarred, but they still get the job done. By the way, Summit Racing.com carries well over a thousand different box end and combination wrenches and wrench sets. We’ll give you a better look at some wrench designs and options in the pics below.

box wrench on a workbench
This is a very common old Craftsman box end wrench from the writer’s tool box. As you can see, it’s 9/16 inch on one end, and 1/2 inch on the other. (Image/Wayne Scraba)
close up of angled head on a box wrench
Different box end wrenches can have different offsets. The offset is really what allows for fastener access. The offset shown here is again, relatively common, but in the next photo you’ll see there can be quite a range between different wrenches: (Image/Wayne Scraba)
old box wrench on a workbench
Here’s a very old double box end the writer acquired from his father’s tool collection (so it’s likely 75 years old or older). It too is a 9/16 and 1/2 inch combination wrench, but the offset is significant. (Image/Wayne Scraba)
close up of angled head on an old box end wrench
The offset on the wrench is considerable. It was likely a specialty tool. More in the next photo: (Image/Wayne Scraba)
90 degree angled heard on a box end wrench
Now that’s an offset! This deep offset actually comes in rather handy for tough to reach nuts and bolts. On the other hand, it’s not really a regular “go-to” tool because it is often clumsy to use. (Image/Wayne Scraba)
old S-K box end wrench on a table
This SK double box end wrench from the writer’s collection is short. It is typically referred to as a “dwarf” because of the length. (Image/Wayne Scraba)
close up of the head of a box end wrench
The offset is conventional and similar to the Craftsman example shown previously. (Image/Wayne Scraba)
Assortment of MAC box end wrenches on a table
All of these combination wrenches (open end, box end) are from the writer’s tool box. They range from an extra-long wrench on top all the way to a stubby on the bottom. Each length has its advantages (and of course, disadvantages). See the article for more insight. (Image/Wayne Scraba)
a pair of MAC box end wrenches on a table
For comparison’s sake, here’s the long and short of it. Ponder the difference in leverage. As you can well imagine, it’s difficult to really get a fastener tight with a stubby but rather easy to over-tighten that same fastener with a long handle. (Image/Wayne Scraba)
a pair of MAC knuckle saver box end wrenches
Different manufacturers have different takes on standard wrench length. Both of these 9/16 inch combination wrenches were the “standard” when purchased. Note the difference in reach with the Mac Tools wrench. (Image/Wayne Scraba)
close up of open heads on a box end wrench
Manufacturers also have different ideas when it comes to open end wrench heads. Note the profile of the open ends here. Mac Tools claims the “Knuckle Saver” design (left) provides for more contact area versus a conventional tool. (Image/Wayne Scraba)
close up of 9/16 box end wrench end
Slight differences also apply to the design of the box end in various wrenches. Obviously, box ends can be 12 point (as shown here) or the less common six point design. (Image/Wayne Scraba)
a pair of 9/16 box end wrench heads
Both box ends are 9/16 inch. The machined configuration is clearly different, but from our perspective, the difference in performance isn’t huge. (Image/Wayne Scraba)
close up of a worn wrench head
Here’s another look at the proprietary “Knuckle Saver” layout in the writer’s Mac Tools open end wrench. The jaws aren’t 100% flat. (Image/Wayne Scraba)
a wright tool box end wrench kit
As pointed out in the story, SummitRacing.com is packed with box end and combination wrenches and wrench sets. This SAE combination set from Wright Tool (part number WTC-715) goes from 5/16 inch all the way up to 1-1/8 inch. You can get sets in both SAE and Metric sizes. (Image/Summit Racing)
a wright tool wrench set mounting board
This double box end set from Wright Tool (part number WTC-D942) covers all of the SAE bases—ranging from 5/16 inch all the way up to 1-1/4 inch. Double box ends like this are often longer than similar combination wrenches. (Image/Summit Racing)
Here’s a very interesting “S” shape wrench from Sunex (part number SXT-9940). The S-curve design provides for maximum access in confined spaces. They are fully polished, drop-forged alloy steel.  (Image/Summit Racing)
special curved box end wrench set
Another interesting take on box ends is this half-moon set from Sunex (SXT-9935). Once again, they’re designed to work in cramped quarters. You might not use them all of the time but when you need one, you’ll be glad you have it! (Image/Summit Racing)
a collection of stubby wrenches
These stubby wrenches from Powerbuilt (part number PWB-640204) are similar to the stubby shown previously. Again, not a regular go-to tool, but simply a specialized application. You can purchase them in metric or SAE sizes. (Image/Summit Racing)
Assortment of box wrenches on a white background
 Recall when we discussed different openings in wrenches? This set of combination wrenches from Sunex (part number SXT-9919MA) makes use of a “V-Groove” design on the open end that is said to reduce wear on fasteners. (Image/Wayne Scraba)
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.