The Anatomy of a Combination Square
Combination squares are often times used in woodworking, however they are highly relevant tools in the work of a machinist. Invented in 1879 by Laroy S. Starrett, the tool became his brand’s first step toward major industry success.
Let’s look at their functionalities as well as which models the Practical Machinist community recommends!
Combination Square Anatomy
What makes the combination square special is its composition. The most common combination square is a two-part tool, comprised of the rule and the “standard” or “square” head. The more souped-up combination square is a made up of a steel rule, 45-degree holder, protractor, and center square.
Image Credit: Starrett
Functionality
In simple terms, this tool will help you achieve accurate measurements of squareness, depth and precise distance from an edge.
For tool makers, the combination square is best for layout work. Providing reliable squareness, precise length and accurate angles that effectively save the toolmaker time and minimize material waste. With combination squares, creating a closely sized square or rectangular piece from large stock can be quick and easy.
The center head is the part of the combination square that allows you to find the center of a piece of round stock, which will be necessary when preparing a work piece for a cylindrical grinder or lathe tail stock.
The protractor head lets you check or set an angle to the closest degree. Once successfully measured, the protractor can be locked in place to secure the reading. The protractor tool is particularly useful in the inspection of large parts with many different angles.
Model Recommendations
We dug through some of our forum threads to gather opinions from the community about different combination square models. Here’s what they recommended.
Included are both the standard head version and the three-part version, depending on your project needs. A protractor, for example, can be looked at as an “add-on” to the standard head if and when necessary. You can find it sold separately here. Other add-ons include a center head, which you can find here.
Standard
IRWIN Tools Combination Square
IRWIN Tools Combination Square, Metal-Body
With a zinc body and stainless steel blade, this combination square is durable and has a comfortable weight.
Starrett C11H-12-4R Combination Square with Square Head
Starrett Steel Combination Square with Square Head
This square head includes a reversible lock bolt, scriber, spirit level, and hardened steel, photo-engraved blade with a satin chrome finish.
Combination
Elitexion 12-Inch Combination Tri-Square Set
12 inches Combination Tri-Square Set
This three-part combination square has a stainless steel rule, a center head and includes a 180-degree protractor.
Mitutoyo 180-906B Combination Square Set
Mitutoyo 180-906B Combination Square Set
The Mitutoyo combination set is well known for its hardened steel parts and versatile measurements.
iGaging 3-Piece 6″ Precision Combination Square and Center Finder Head
iGaging Combination Square Premium 3-Piece 6″ 4R Center Head
Featuring a satin chrome finish, this set has both a comfortable feel and weight and provides accurate and smooth measurements.
Brown & Sharpe 599-439-1204 Combination Square Set
TESA Brown & Sharpe 599-439-1204 Combination Square Set
Note that the center head and square head are not hardened. The protractor is reversible. This set is known for its well finished parts, so you never have to worry about cutting your hand.
Starrett C435-12-4R Combination Set, Cast Iron Heads, Satin Chrome Blade
Starrett Combination Set with Square, Center and Reversible Protractor Head and Blade
The delicate nature of this tool requires careful handling. User reviews note the beauty of this tool, but it’s definitely for machinists looking to splurge.
Accusize Industrial Tools 12” 4 Combination Square Ruler Set Protractor Satin
Accusize Industrial Tools 12” 4 Combination Square Ruler Set Protractor Satin
Includes fully hardened blades with satin chrome finish and is considered high quality at a reasonable price!
This post may contain affiliate links. Please read our disclosure for more info.
1 Comment
Based on long experience of supplying the metal working trades, specially steel fabricators, I feel that this article should mention that only combination squares with hardened steel heads are suitable for structural steel workers as hot rolled steel makes the heads wear and lose their accuracy very quickly.
I believe that aluminium heads are OK for woodworking and other applications but I don’t have much experience in this field.