Buying guide for best combination squares
A good combination square is an invaluable addition to any toolbox – but which one should you purchase? There are hundreds to choose from, and the prices run the gamut.
Each of our top five combination squares offers a great choice of features and excellent value. We're happy to recommend them in the table above. If you'd like to know more about how we came to our decisions, please read on.
Why buy a combination square?
An accurate woodworker's or engineer's square is a valuable part of any toolbox. It allows you to check quickly if something is square – but that's really all it does. Some have graduations for measurement, but they are of limited use.
A combination square is much more versatile. It can be used to check 90-degree or 45-degree angles. Some come with protractor heads that measure other angles. Different lengths can be set, making it useful for marking. The blade, which can be used separately as a rule, is usually much longer – 12 or 16 inches – whereas an ordinary square is six inches or less.
"The blade of a combination square is much more rigid than a tape, so on smaller jobs, it's easier to be precise when marking."
STAFF
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Construction and features
At first glance, the combination square appears to be a simple tool. However, the materials used and the way it's put together make a big difference in how accurate it is and how long it lasts.
The majority of combination squares are composed of the following.
Let's look at each in more detail.
Blade
The blade, in combination with the head, are the two major components of a combination square. Quality of construction in both cases goes a long way toward defining the accuracy of the finished tool.
All blades are steel, but better ones are hardened and tempered, extending their life. Similarly, markings that are etched into the surface don't get worn away. The graduations offered can vary down to 1/64th of an inch in some cases. Metric versions are also available. Rigidity is important to long-term accuracy, so the thicker the blade, the better.
Head
The head is extremely important. Not only does it have the main bearing surfaces for gauging 45 and 90 degrees, it also has the slot through which the blade passes. If that doesn't run true and at a precise right angle, the tool will never be accurate. A machine screw is used to lock the blade in place.
Quality here is everything. On cheap combination squares, the head is often made of die-cast alloy (frequently just called "metal"). That’s not a problem in itself if it has been finished properly. Unfortunately, this is often not the case with low-cost tools.
Better-quality heads are made from cast iron, which is extremely tough and resistant to oils and chemicals. The very best heads are made of forged and hardened steel, precision ground. It's an engineering tool rather than a woodworking one, and considerably more expensive.
Bubble vial
A small bubble vial allows you to use a combination square as a spirit level. It's often nice to be able to check that something is level as well as square. Given the length of the head that it's built into, however, there are limits to its accuracy. If you need to check level over any distance, it's advisable to use a laser level or a traditional model.
Scriber
The scriber is usually inserted into the back of the combination square. It's a short, steel point that can be used to mark lines on all kinds of surfaces. Its main advantage is that it marks a finer, more accurate line than a pencil, and the mark doesn't get blurred or erased by handling.
The downside is that the mark is made by scratching into the material, so it's not easy to remove later if necessary. It's also quite small, so those with large fingers might find it difficult to use.
Feature variations
There are a couple of possible variations on features to consider. Some combination squares also come with a protractor head, a center finder, or both.
Protractor heads can be used to set and mark angles. While generally limited to 180 degrees, some are marked on both sides and can gauge a full 360 degrees by being flipped over. Not all tools have this feature, so check before ordering if it’s important to you.
A center finder is a fixed V shape with a 90-degree angle inside the V. This is attached to the blade. When the open end of the V is placed against the edge of a round object, the blade indicates the center.
Although these are reasonably robust tools, a bent blade or damaged head is likely to cause inaccuracies. For that reason, a protective case is always a nice extra.
FAQ
Q. Is there an easy way to tell if my combination square is actually square?
A. Yes, there is. Rest the head against a block of wood, and extend the blade as far as possible to form a standard, L-shaped square. Use the scriber or a pencil to mark a line along the blade. The longer the line, the greater the accuracy. Now, flip the tool over so the other side of the head rests against the block. Push the blade up to the line you marked. It should meet. If it forms a V shape, then it's not properly square.
Q. Why are some combination squares a lot more expensive than others?
A. It comes down to the quality of the components, which define the precision of the instrument. Each of the elements mentioned above impacts accuracy and durability.
If a combination square is something you'll only use occasionally, a budget model would probably suit you fine, though accuracy might be a little off. If you use a combination square regularly, however, it's worth making the extra investment.
Q. Thumb screws are often brass. Is there a reason for this?
A. Brass has a quality feel and doesn't rust. However, because it's relatively soft, it's usually just a decorative top. Underneath, there's a hardened steel machine screw.
