The Sterling Double Square and Dovetailing Rule is a high quality measuring and marking set that is typical of the high quality of other Sterling products that I have reviewed here . The double square is supplied with a 4 inch graduated rule that has a chrome satin finish with lines and numbers etched in black. I highly recommend etched rules so that you can precisely set up other marking devices, like a compass, by feeling them register in the etched markings. The etched rule has an advertised accuracy of 0.001" per inch.

The Dovetailing Rule was developed to check the squareness of the various surfaces of a dovetail joint. The dovetail rule does not have any etchings on the surface but has two different widths for angling into various parts of the dovetail as I'll show later. A regular size rule cannot get into the small spaces of a dovetail joint, especially if you are hand cutting very small dovetails.

One side of the rule is marked off in 1/8" and 1/16" increments. The other side contains divisions for 1/32" and 1/64" increments. These are shown in the following pictures. I found it very easy to loosen the thumbscrew and either move the rule back and forth or to flip it around, if necessary. The adjustment feels 'precision ground' with no play (wiggle).

Why a 4" rule when you may already have a 6" or 12" Combination Square ? I like the fact that I can always have it close at hand and that makes it very convenient to use. I'm always reaching for mine to make small measurement marks or to test an edge. I have it ready in the front pocket of my apron which makes it very convenient to use.

As you can see, it easily fits into the front pocket of my shop apron. It is always close at hand!

Here are a few examples of how I use the Double Square in my shop. It has the normal use of making precise measurements near the edge of a board.

I will sometimes chip carve borders along the edge of a board and this makes it very easy to draw lines parallel to the edge. I also use it to check the squareness of an edge. For example, if I'm hand jointing the edge of a board I can quickly pull out the square and run it along the edge of the board and see if it angles one way or the other. The following picture shows an edge that is lower on the left side.

The 4" Square is very easy to hold which makes it very easy to run along the edge as compared to trying to do the same thing with a 12" Combination Square. You also can't quickly reach into your shop apron and pull out a 12" Combination Square!

The Double Square set also comes with a Dovetailing Rule to measure the squareness of a dovetail joint. Depending on what surface you want to test, you can use either the wide or narrow blade of the rule. The rule in the first picture is testing the bottom surface of the joint. This area is relatively large so I can use the wider blade.

Below is how it would look from the back side. You can see that the blade fits nicely across the bottom of the dovetail joint and it's easy to see that it's flat. You can rock it across the surface looking for any bumps or hills that will obstruct the pins from sliding into the joint.

Now, to test the opposite end of the dovetail joint requires switching to the narrow blade. Since it is a Double Square, you just need to turn the square around.

First test one surface and then slide it across and test the adjacent surface.

Very easy, very quick, yet very precise!

Finally, like Combination Squares, the Double Square can help during tool setup to check a blade for square to the tool's table. When I do precision setup of a tool I'll use a 12" Combination Square because the long blade gives a high degree of accuracy when placed against a long surface of a saw blade. However, if I'm coming up to my bandsaw, for example, with a relatively thin workpiece, I'll reach into my pocket and use the Double Square to do a quick check of the blade to make sure that the portion of the blade being used during the cut is square to the table. It takes almost no time at all and I have the assurance that I'm going to get a square cut.

Like most woodworkers, I have plenty of tools hanging on the walls or stored in a cabinet and I can reach for them whenever I need to use one. Then there are the tools that you keep in your apron pockets because you want them close at hand and you use them frequently throughout the day. The Sterling Double Square is one of those "keep close at hand" tools. You will definitely increase the quality of your dovetail joinery by using the Dovetail Rule. This is one tool you definitely want to add to your shop.

Jeffrey Fleisher has been a woodworker for approximately 20 years and a professional woodworker for the past 6 years. He is the president of his local woodturning club, the Woodturners of the Virginias and past president of the Northern Virginia Carvers. You can see some of the furniture he has made at www.jeffswooddesigns.com . He can be reached by email at furnmkr@gmail.com