Speed square

How it works

The user seats the fence of the square against the edge of a board and draws along the other leg for a square mark, or along the hypotenuse for a 45° mark. A heel on the fence holds the square against the board edge, and the same heel can guide a circular saw base for a straight cut.

For rafters the square is pivoted about one corner against the board edge until a number on the common-rafter scale lines up with the edge. A line drawn along the leg is then the plumb cut at the ridge. Swanson calls the method the One Number method: the framer reads the pitch from the plan once and uses the same number for every rafter on the roof.

Lengths are computed from the run of the rafter and a multiplier for the pitch. Swanson’s reference for a 4/12 pitch gives a multiplier of 1.0541 times the run for the common rafter length before any tail is added.

Anatomy

Body: A right-isosceles triangle. Swanson’s 7 inch square is heavy-gauge CNC-machined aluminum alloy; the company describes the original of 1925 as a stamped aluminum plate with a riveted base.
Fence (heel): A raised edge along one short side, 7/8 inch on Swanson’s 7 inch square, that holds the tool against a board edge and guides a saw.
Scribe bar: A 1/4 inch bar on Swanson’s 7 inch square that rips parallel layout lines from the same edge; the company says Ronald C. Swanson added a milled scribe bar to the Big 12 in 1975.
Scales: Degree scale, common rafter scale, and hip/valley rafter scale, per Swanson’s specification.
Pivot point and diamond cutout: The corner on which the square pivots; Swanson’s 3 1/2 inch diamond-shaped cutout along the centerline marks a one-motion seat cut on common, hip and valley rafters.

Variants

7 inch Speed Square: The standard size.
Big 12: A 12 inch square with a scribe bar and a 12 inch ruler edge, and a Layout Bar for stair stringers and long rafter cuts, per the Blue Book contents.
Metric Speed Square: Swanson’s 25 cm square with metric gradations and 0.5 cm scribe notches.
Pro Speed Square: A newer model that Swanson describes as the standard of the industry.
Trim and Speedlite squares: Smaller layout squares and a level-square listed in Swanson’s range.

Specifications

Size (common) · in: 7 inSwanson’s 7 inch square has a 7/8 inch heel, a 1/4 inch scribe bar and weighs 0.68 lb.
Scales: Degree, common rafter, hip/valleyPer Swanson’s specification for the 7 inch square.
Material: Aluminum alloySwanson describes its current squares as CNC-machined heavy-gauge aluminum alloy with deep black-filled markings; the company’s own statements.

Tips

Use one number for every rafter
The phrase stamped on the original, “use same number all cuts this roof,” states the One Number method: read the pitch from the plan once and use the same number on the common-rafter scale for every cut on the roof, as Swanson describes it.1
Pivot the square for the ridge plumb cut
Swanson’s instruction for a 4/12 roof is to pivot the square on the top edge of the rafter, align 4 on the common scale with the edge, and scribe the plumb line, which is the ridge cut. A second plumb line at the seat, plus a level line the width of the top plate, gives the bird’s mouth.1
Cut a pattern rafter first
Swanson advises cutting one rafter as a pattern, test-fitting it against the ridge and the top plate, and using it as the template for the rest, and never cutting a stack from the numbers alone.1
Run the heel along the edge as a fence
The heel holds the square against the board edge for square and 45° marks or to guide a circular saw, and the scribe bar rips parallel lines from the same edge, according to Swanson’s product description.1
Use the diamond cutout for seat cuts
Swanson’s diamond cutout, a 3 1/2 inch opening along the centerline, was introduced in 1992 as a faster pivot for scribing seat cuts, and the company says it marks a seat cut in one motion on common, hip and valley rafters.1 2

History

Earliest documented

1925

Chicago, Illinois

Swanson Tool Co. says that Albert J. Swanson, a Swedish-American carpenter who came to Chicago from Iowa in 1920, perfected the first Speed Square in 1925, a triangular aluminum layout tool combining a try square, miter square, saw guide, line scriber and protractor. The company dates a published advertisement to American Builder, April 1927, by the Swanson Square Company of Maywood, Illinois. No patent record or independent source for the 1925 date has been located.1

Everything sourced for the speed square comes from its maker. Swanson Tool Co. is the only party whose history of the tool could be read, and the dates and statements below are the company’s, not independent findings. The company says Albert J. Swanson, a carpenter working on the Drake Hotel in Chicago, perfected the first Speed Square in 1925 and that the original was a stamped aluminum plate with a riveted base; its page also lists the material of the original as die-cast aluminum alloy, and the two statements are not reconciled.

The tool was meant to replace several tools. Swanson describes it as a try square, a miter square, a saw guide, a line scriber and a protractor in one piece. Its distinctive function is the rafter scale: by pivoting the square about its corner on a board edge to a number marked on the common-rafter scale, a carpenter reads off the plumb and seat angles for a rafter without calculating them. Swanson calls this the One Number method, and says Albert Swanson packed a pocket “Blue Book of Rafter Lengths” with the square from the first.

Distribution followed. The company says Montgomery Ward licensed the tool under its Lakeside brand in 1930 and that ownership returned to Albert Swanson shortly after, that he incorporated Swanson Tool Company in 1945, and that the square was asked for by name. The same history says its present family (the Big 12 with a scribe bar added in 1975, the diamond cutout of 1992, metric, trim and pro models) rests on the original geometry.

The materials and manufacturing moved from stamping to machining. Swanson states that every current square is CNC-machined from heavy-gauge aluminum alloy, with markings recessed and filled black, and argues that this keeps the markings legible and the corner square under abuse. These are product claims; no independent test of the tolerance or durability of speed squares, of Swanson’s or of its competitors, was located.

Timeline

1920
Albert J. Swanson moves from Iowa to Chicago and joins the crew finishing the Drake Hotel, according to Swanson Tool Co.1
1925
Swanson perfects the first Speed Square, which the company says it hand-filed after three years of refinement, and begins making them for other carpenters on his crew.1
1927
An advertisement for the Speed Square by the Swanson Square Company of Maywood, Illinois, appears in American Builder, April 1927, which the company calls one of the earliest published advertisements.1
1930
Montgomery Ward of Chicago licenses the tool for its catalog under the Lakeside brand, the first appearance of the square in interstate commerce, according to the company.1
1945
Swanson Tool Company is incorporated.1
1975
Ronald C. Swanson designs and patents a scribe bar along the long edge of the Big 12 Speed Square, per the company.1
1992
The 3 1/2 inch diamond cutout is added to the Speed Square.1
2014
Swanson adds a full marking line, with pencils, plumb bobs, chalk lines and lumber crayons.1

Where the sources disagree

What was the original 1925 Speed Square made of, and was it patented in 1925?

The original was a stamped aluminum plate with a riveted base; Albert Swanson patented the design in 1925 (“same design Albert Swanson patented in 1925”).1
Swanson Tool Co., Our Story page, text of the invention and introduction
The material of the original is die-cast aluminum alloy; the timeline says Swanson “files the first die” in 1925 and does not mention a patent.1
Swanson Tool Co., Our Story page, specification panel and timeline

Gaps in the record (6)

Albert Swanson’s patent, if one exists, was not located; the patent number, grant date and claims are missing, and the company’s statement that the design was patented in 1925 is unverified.
No independent source for the 1925 date, the 1927 advertisement or the 1930 Montgomery Ward license was located.
Predecessor rafter squares and triangle squares before 1925 are not documented here.
No standard for speed square accuracy was located; standards is empty.
Safety and care have no sourced entries.
Competing makers’ histories were not examined.