Mastering Precision: How to Use a Combination Square Like a Pro

As a master woodworker, I often get asked about the usefulness of the combination square. This simple yet versatile tool has become an indispensable part of my workshop. In the right hands, the combination square can make precise measurements, mark straight lines and perfect angles, and ensure your projects always come out “square.”

The combination square consists of a ruler blade attached to a handle, with parts called the shoulder and anvil used for measuring. To use it properly, you first need to understand its structure and functions. The shoulder places the square at 45 degrees while the anvil provides a 90 degree angle. Other parts like the bubble level also have specific purposes.

With a sturdy metal construction, the combination square can provide years of reliable service. This introduction will walk through the most common uses of this tool to fully utilize its potential. We’ll cover how to check for square, mark angles, set depths, and other handy tricks. A quality combination square is affordable and will quickly prove itself as a woodworking must-have. So let’s get started and see how this simple tool can bring precision and accuracy to your workshop projects.

What is a Combination Square?

A combination square consists of several key components:

  • Blade/Ruler – This is the ruler part that has imperial or metric measurements marked on it. It allows you to make precise marks and measurements. The blade is typically made of stainless steel for durability.
  • Head – The head attaches perpendicularly to the blade and has two surfaces:
    • Anvil – The anvil attaches at a 90 degree angle to the blade. It allows you to mark perfect square lines and check for square on your workpieces. The anvil will have a small lip that comes into contact with your material.
    • Shoulder – The shoulder attaches at a 45 degree angle to the blade. It’s used for marking angled cuts like miters. The shoulder is generally a simple beveled edge.
  • Locking Mechanism – This tightens the head in place on the blade. A knurled knob allows you to easily secure or adjust the head. Make sure this locking mechanism works smoothly.
  • Bubble Vial – Many combination square heads will have a small circular bubble vial that assists with leveling or finding plumb. It can be used in conjunction with the anvil or shoulder.

Combination squares come in common sizes like 6″, 12″, and 24″. The most popular size for general woodworking is the 12″ combination square. The ruler part usually has both metric and imperial units marked, with inches on one edge and centimeters on the other. High-end squares will often etch the markings into the blade for durability.

Checking for Accuracy

Before using a new combination square, you’ll want to check that it’s properly calibrated. An inaccurate square will lead to poor work and frustration.

Here is how to properly check a combination square for accuracy:

  1. Find a known-flat surface like your table saw top or workbench. This will serve as an accurate reference surface.
  2. Place the anvil of the combination square directly against the flat reference surface. Make sure the anvil is sitting flat with no gaps.
  3. With a sharp pencil, draw a straight line along the edge of the blade. Make the line as long as possible for better accuracy.
  4. Now flip the combination square over, keeping it in the same orientation. Place the straight ruler edge directly over the line you just drew.
  5. Holding the square firmly in place, draw a second line along the edge of the blade.
  6. If the two lines perfectly overlap, your combination square is properly calibrated and ready for use. Minor variations can be adjusted with the locking knob.
  7. However, if the two lines are misaligned or do not match up, your combination square needs calibration or possibly replacing altogether.

Checking your square every so often is a good habit to ensure you are getting perfectly square marks and measurements in your woodworking projects.

Common Uses

Here are some of the most common uses for a combination square:

Checking for Square

  1. Place the anvil against one edge of the material you want to check.
  2. Lay the blade against the adjacent perpendicular edge.
  3. If the blade isn’t perfectly flush with no gaps, then your material isn’t square.
  4. You can also slide the square into an interior corner to check for square.

Marking 90 Degree Lines

  1. Place the anvil firmly against the edge of your workpiece or other known straight edge.
  2. With your pencil at the end of the blade, slowly pull the square away and draw a line toward the anvil.
  3. This will give you an accurate 90 degree line for joinery, cross-cutting, assemblies, etc.

Marking 45 Degree Lines

  1. Place the shoulder firmly against the material edge. Ensure full contact.
  2. Just like above, use a pencil at the end of the blade to slowly draw a line toward the shoulder.
  3. You now have an accurately angled line for miters. Repeat on your miter saw workpiece.

Measuring Depths and Thicknesses

  1. Place the anvil flat on one surface to be measured.
  2. Position the blade on the opposite surface and lock the head securely.
  3. The measurement along the blade to the anvil is the exact depth or thickness.
  4. Use this for mortises, tenons, material thickness, rabbets, etc.

Scribing Parallel Lines

  1. Extend the blade to your desired offset dimension and lock the head.
  2. Place the anvil against the edge you want to run parallel to.
  3. As you slide the square along, the extended blade will scribe a perfectly parallel line.
  4. Useful for joinery and fitting pieces together.

Setting Up Tools

  1. Use the blade to set exact depths for table saw blades, router bit heights, drill press stops, etc.
  2. Easily adjust miter saw angles by placing the anvil or shoulder against the blade and adjusting to the square.


  1. The bubble vial on some combination square heads allows you to find level or plumb.
  2. Place the anvil on a surface and adjust until the vial shows level.
  3. Can also determine if fence posts, cabinets, etc. are plumb.

As you can see, the list of uses goes on and on. The combination square is one of the most versatile tools for layout and measurement.

Maintenance Tips

Follow these tips to keep your combination square in top shape for years:

  • Avoid dropping it or using it as a hammer or pry bar. This can bend the ruler or ruin the precisely machined surfaces.
  • Keep it lightly oiled with a penetrating oil to prevent rust or corrosion, especially if using it outdoors. Wipe down before use.
  • If markings become difficult to read, carefully go over them with a permanent marker to restore the visibility.
  • Consider having multiple combination squares stationed around your workshop. You’ll always have one on hand and won’t have to walk across the shop to find it.
  • Check calibration periodically by scribing lines. This also confirms your workspace itself is level.
  • Adjust the locking mechanism if it becomes loose or hard to secure the head. Replacement parts are available.
  • Store the square neatly along with other measuring tools. Keep it in a tool roll or case when not in use.

Properly cared for, a quality combination square should deliver years of use. It’s a worthwhile investment for every woodworking shop.

Alternate Designs

While the standard combination square is the most common, there are some other designs worth mentioning:

  • Multi-Squares – Heads that have multiple anvils and shoulders in different sizes for more flexibility. Great for stairs and complex angles.
  • Wooden Combination Squares – All wood construction instead of metal. A bit more delicate but nice for fine furniture work. May come with two heads.
  • Metric Only – Squares with only metric measurements as opposed to imperial/metric combo squares. Handy for Metric-only projects.
  • Engineer’s Square – A smaller and lighter pocket-sized square. Easy to keep in a tool belt or pocket.
  • Framing Square – Larger steel squares with 24″ blades used for construction and framing. Have various calculation tables.
  • Speed Square – Triangular piece of metal that combines the functionality of a rafter square and combination square.

Even basic combination squares have evolved to include additional holes and marks for functions like calculating stair stringer layouts. There are many options, so choose the combination square design that best fits your needs.

Comparison Table of 4 Popular Combination Squares

Feature iGaging Bench Square Set Irwin Combination Square Johnson Level & Tool Square Swanson Combination Square
Size 7″ and 12″ squares 12″ square 12″ square 12″ square
Construction Stainless steel Chrome-plated brass Aluminum Stainless steel
Accuracy Decent Very accurate Reasonably accurate Highly accurate
Ease of Use Smooth adjustments Easy to adjust and lock Stiff adjustment knob Smooth adjustments
Durability Average Durable Aluminum can scratch Very durable
Price $$ $ $$ $$$
Overall Rating 3/5 4/5 3/5 5/5

Frequently Asked Questions about Using Combination Squares

How do I know if my combination square is accurate?

You can check a combination square for accuracy by drawing a line with it, flipping it over, and drawing a second line. If the lines match up, the square is accurate. If the lines don’t match, the square needs to be replaced.

What size combination square should I get?

The two most popular sizes are 6″ and 12″. 12″ is the most common for general woodworking purposes. Larger squares like 24″ are used more for construction.

Can I use a combination square to mark angled lines?

Yes, the shoulder on the square head allows you to mark 45 degree miter lines. Some squares also have additional markings for other angles.

How do I read the metric measurements on a combination square?

Metric measurements are usually on the opposite edge from the imperial units. Look closely and you’ll see mm or cm marked between the inch increments.

Should I oil my combination square?

Yes, you can apply a light machine oil periodically to prevent rust, especially if using it in damp conditions. Wipe it down before using.

Can I hammer with a combination square?

Never use a combination square as a hammer or pry bar, as it can damage the precision machined surfaces. Use it only for its intended purposes.

Why do my ruler markings look faded?

You can carefully go over faded markings with a fine permanent marker to improve visibility. Avoid using solvents.

How do I adjust a loose combination square head?

There is typically a locking nut or knob that can be tightened to secure the head from moving. Be careful not to over tighten.

Should I buy plastic or metal combination squares?

Metal is much more durable for shop use. Stainless steel or brass are good options. Avoid cheaper plastic or aluminum squares.

Wrapping Up

With its versatility and precision, the combination square is an invaluable addition to any woodworking toolkit. By mastering its use for checking square, marking perpendicular and angled lines, setting depths, and more, you’ll find this simple metal tool pays dividends in the accuracy and quality of everything you build. Take time to learn the different components, confirm the square’s accuracy, and practice its techniques on scrap material. Store it properly when not in use and keep the blade oiled for protection. While basic in appearance, the functionality and convenience of a combination square will be quickly realized as your go-to layout and measurement instrument. Allowing you to work faster, smarter and more accurately, the combination square will surely become a trusted companion in your shop.

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