Every serious framer hits the same wall eventually: a speed square is brilliant for common rafter plumb cuts, but the moment a hip, valley, or jack rafter demands a compound cheek cut, the standard pivot-and-mark method falls apart. The side cut angle hides in trigonometry, not in the simple degree scale, and guessing a 22.5- or 45-degree visual reference leaves you with gapped joints and wasted lumber. The solution is the TrigJig, a clip-on speed square trig accessory that turns the humble rafter square into a precision compound-angle layout tool.
This article is the ultimate guide to pairing a speed square with the TrigJig, covering the mechanics, the workflow, and the exact rafter table numbers that make the system work. It is also a practical buying guide for the best speed squares to mount the TrigJig on, so you’ll know exactly which tool to grab for your next roof. Expect an exhaustive analysis of compound rafter geometry, step-by-step layout instructions, and the common mistakes that separate clean structural joints from frustrating re-cuts.
The Short Answer: Why the TrigJig Changes Everything
The TrigJig is a patented accessory that mounts directly onto a 7-inch Swanson-style speed square and transfers the square’s printed rafter tables into a physical, adjustable scribing angle. Instead of pulling out a framing square or doing sine-cosine math on the tailgate, you set the speed square to the roof pitch, slide the TrigJig to the hip/valley rafter number, and scribe a line that is exactly the compound side cut you need. For anyone cutting jack rafters, hip rafters, or valley rafters on a regular basis, the TrigJig eliminates the guesswork and improves the accuracy of every layout.
The recommended platform is a genuine Swanson 7-inch speed square or a high-quality aluminum clone with clearly embossed rafter tables. Below is a quick look at the top speed squares to consider for TrigJig use, with a full feature comparison later in the article.
| Product | Key Feature | Price | Rating | Buy |
|---|---|---|---|---|
 |
Swanson Speed Square Pro 7″ (S0100) – Made in USA, black embossed scales, pro-specific guide | $14.98 | 4.8 | Buy at Amazon |
 |
Swanson SW1201K Value Pack 7″ + Big 12 Speed Square – Two squares, ultimate precision | $16.50 | 4.8 | Buy at Amazon |
 |
Swanson S0101 7-Inch Speed Square Blue – Classic aluminum alloy workhorse | $9.98 | 4.8 | Buy at Amazon |
 |
7-Inch Aluminum Rafter Square (Double-Sided Engraved) – Budget-friendly, precision etching | $5.99 | 4.6 | Buy at Amazon |
 |
Aluminum Alloy Rafter Square 7-Inch (Laser-Etched, Red) – Laser-etched scale, multi-angle protractor | $7.99 | 5.0 | Buy at Amazon |
For those in a hurry: buy the Swanson S0101 if you want a proven, inexpensive platform for the TrigJig, or step up to the Swanson Speed Square Pro S0100 for a more robust body and easier-to-read black embossed scales. Both are manufactured in the USA and work perfectly with the TrigJig’s mounting clips.
Understanding the Core Mechanics: What the TrigJig Speed Square Accessory Actually Does
The TrigJig is not a replacement for a speed square; it is a precision add-on that clips against the square’s body and lets the user dial in compound angles using the printed rafter tables. In its simplest form, the device has a sliding scale, a cam lock, and a scribing edge that moves relative to the square’s pivot point. When locked, the TrigJig holds the square at the correct rotational offset for a given rafter condition, converting the square’s standard pitch settings into the true geometric angle of a side cut.
The brilliance of the system is that it solves the most confusing part of rafter layout: the difference between the plumb cut angle and the side cut angle. The pitch of a roof gives you the plumb cut on a common rafter, but a jack rafter meets a hip or valley rafter at a compound angle because the two rafter planes intersect in three-dimensional space. The TrigJig uses the same rafter table numbers printed on a Swanson square, so the framer never has to perform a single trigonometric calculation.
Because the TrigJig is engineered around the Swanson 7-inch square geometry, the best speed square for the job is one that conforms to that classic profile. The big, heavy-gauge Swanson SW1201K Value Pack is a smart choice because it includes both a 7-inch square for TrigJig compatibility and a 12-inch Big 12 square with its own layout bar for marking common and hip rafter lines on wide stock.
Why Standard Speed Square Layout Fails on Compound Rafter Cuts
A standard speed square is excellent at two tasks: drawing a straight 90-degree line and marking a plumb cut at a defined pitch. When you rotate the square to the roof pitch, say 6/12, you are positioning the pivot at the top of the rafter and scribing a line that represents the angle of the rafter against the ridge board. The problem emerges when that line has to be cut at a diagonal approach angle, because the wide face of the rafter is not perpendicular to the line of the hip.
A hip rafter runs at a 45-degree diagonal in plan view, so its effective slope is shallower than the common rafter slope. A jack rafter that lands into that hip must have a plumb cut and a side cut that work together, forming a pointed, multi-faceted joint. Without a specialty tool, most DIYers either compensate by holding a bevel gauge against the rafter table or simply mark a 45-degree line and hope for the best. The result is a sloppy joint that requires shimming, caulking, or additional blocking.
The TrigJig resolves this by turning the speed square into an adjustable hip-valley square. It takes the rafter table’s “hip or valley rafter per foot run” value and translates that directly into the correct side cut angle. This is why the accessory has become a staple for serious roofers and advanced DIYers who need clean joints without pulling out a full framing square or a construction calculator.
The TrigJig Speed Square Workflow: Step-by-Step
To get accurate, repeatable results, follow the TrigJig workflow exactly as described below. The system assumes you have a 7-inch speed square, the TrigJig accessory, and a clear understanding of your roof pitch.
Step 1: Attach the TrigJig to a Compatible 7-Inch Square
Mount the TrigJig onto the long body of the speed square so its sliding arm rides smoothly against the square’s back edge. The Swanson Speed Square Pro S0100 is ideal for this task because its flat body and crisp black embossed scales make the alignment marks easier to see while the accessory is locked in place. Make sure the TrigJig’s reference marker lines up with the scale on the square’s body before you take any measurement.
Step 2: Identify the Roof Pitch and Read the Rafter Table
Determine the roof pitch in inches of rise per foot of run. If you are working with a 6/12 pitch, check the rafter table printed on the face of the speed square. The line labeled “Length of Hip or Valley Rafters per Foot Run” is the number you need. For a 6/12 roof, that value is 18.00 inches. For an 8/12 roof, it is approximately 18.76 inches. Write this number down so you can set the TrigJig without hunting for it again.
Step 3: Set the TrigJig Scale to the Hip/Valley Rafter Value
Slide the TrigJig’s marker until it points to the hip/valley rafter value you found in Step 2. For a 6/12 roof, align the marker to 18.00. Lock the cam or thumbscrew firmly. The accessory is now set to the exact compound angle required for a jack rafter intersecting a hip or valley at a 45-degree plan angle.
Step 4: Position the Square and Scribe the Cheek Cut
Place the speed square’s pivot at the top edge of the rafter stock, just as you would for a common rafter plumb cut, and rotate the square to the roof pitch line on the common scale. With the TrigJig locked in place, hold the square tight against the lumber and scribe along the TrigJig’s edge with a sharp pencil or a marking knife. The resulting line is the side cut for the jack rafter, not the plumb cut, and it accounts for the diagonal approach angle automatically.
Step 5: Transfer, Cut, and Verify with a Test Fit
Mark both faces of the rafter using the same setting, then cut with a circular saw or miter saw set to the appropriate bevel angle. Before cutting a full production set, always make a test cut on a scrap piece of the same dimensional lumber. Dry-fit the test piece against the hip or valley rafter to verify the compound angle, then transfer the settings to your actual rafter stock. This verification step is the difference between a clean production run and a pile of mis-cut lumber.
Rafter Tables Demystified: Using the Hip and Valley Rafter Numbers
The rafter tables on a speed square are printed in tiny, dense type along the body, and most users ignore them entirely. The first data line, “Length of Common Rafters per Foot Run,” gives the hypotenuse of the rafter for each pitch; for 6/12, that is 13.42 inches per foot of run. The second line, “Length of Hip or Valley Rafters per Foot Run,” gives the true length of a rafter running at a 45-degree diagonal in plan; for 6/12, that is 18.00 inches per foot of run.
The TrigJig leverages this second number to correct the side cut angle. Rather than using the degree scale on the square, the accessory converts the hip/valley rafter length into an angular offset that matches the roof geometry. This is why the tool works across different pitches without any formula work. You simply read the table, set the marker, and scribe.
| Roof Pitch | Common Rafter per Foot Run | Hip/Valley Rafter per Foot Run |
|---|---|---|
| 4/12 | 12.65 in | 17.09 in |
| 6/12 | 13.42 in | 18.00 in |
| 8/12 | 14.42 in | 18.76 in |
| 10/12 | 15.62 in | 19.70 in |
| 12/12 | 16.97 in | 20.78 in |
Every Swanson S0101 carries these tables in the classic blue aluminum body, which is why this square remains the default recommendation for TrigJig users. The tables are molded into the aluminum in a dark blue finish that is easy to read even in low afternoon light.
Key Differences at a Glance: Choosing the Best Speed Square for TrigJig Use
Not every speed square is equally suited to the TrigJig. Build quality, edge profile, scale legibility, and the presence of a proper pivot notch all affect how well the accessory locks on and how accurately it transfers the rafter table values. The table below compares the five speed squares from this guide so you can make an informed decision.
| Product | Material & Build | Scale Visibility | TrigJig Compatibility | Best For | Price | Buy |
|---|---|---|---|---|---|---|
|
Swanson Speed Square Pro 7″ (S0100) – Heavy-gauge aluminum, USA-made | Black embossed scales on bare aluminum, excellent contrast | Excellent – flat back edge, standard pivot | Professional framers who want maximum legibility and a pro guide | $14.98 | Buy at Amazon |
|
Swanson SW1201K Value Pack – 7″ plus Big 12, aluminum | Classic blue body on both squares | Excellent on 7″ square; Big 12 used for long rafter marks | Users who need both compact layout and full-width rafter layout | $16.50 | Buy at Amazon |
|
Swanson S0101 7-Inch Speed Square Blue – Classic aluminum alloy, USA-made | Dark blue finish with black scales | Excellent – the industry baseline | All-purpose framing and TrigJig use on a budget | $9.98 | Buy at Amazon |
|
7-Inch Aluminum Rafter Square (Double-Sided) – Double-sided engraved scales | Engraved lines, decent contrast | Good – check edge tolerances on budget units | Budget-conscious DIYers and occasional roof repairs | $5.99 | Buy at Amazon |
|
Aluminum Alloy Rafter Square 7-Inch (Laser-Etched, Red) – Laser-etched red finish | Laser-etched, fine detail | Good – verify edge flatness | Craftsmen who want a compact multi-angle protractor | $7.99 | Buy at Amazon |
If you want the best overall performance for a TrigJig setup, the Swanson Speed Square Pro S0100 is the top pick. Its black embossed scales stay legible even after years of abuse, and the included pro-specific user guide covers advanced rafter applications that the standard blue square lacks.
Best Use Cases for Each Speed Square Model
Choosing between these five speed squares depends on the type of work you do, the lumber sizes you handle, and whether the TrigJig will live permanently on a single square or need to be swapped frequently.
Swanson Speed Square Pro S0100 – The Professional Daily Driver
The Pro S0100 is the most refined Swanson square available, with a heavier gauge body and a black-on-bare-aluminum finish that resists hiding scribe lines. This is the square to keep permanently mounted with the TrigJig, because the high-contrast scales make it easy to read both the pitch setting and the TrigJig reference marker at a glance. Its 4.8-star rating across over 1,300 reviews reflects its popularity with working carpenters.
Swanson SW1201K Value Pack – The Two-Tool Workstation
For the framer who wants a dedicated TrigJig square and a separate long-layout tool, the SW1201K bundle is exceptional value. The 7-inch square covers all pocket and cheek cut work with the TrigJig, while the Big 12 square handles full-depth rafter lines and wide beam marking. At $16.50 for two heavy-gauge aluminum squares, this pack outperforms single premium squares in versatility and convenience.
Swanson S0101 Blue – The Reliable Classic
The blue S0101 is the square that most other accessories are designed against, including the TrigJig. It is stamped from the same aluminum alloy as the Pro model and carries the standard rafter tables in an easy-to-read dark blue finish. With more than 17,200 reviews and a 4.8 rating, it is the value champion for DIYers who need a dependable TrigJig platform without spending extra on pro-specific features.
7-Inch Aluminum Rafter Square – The Budget Entry Point
The double-sided engraved square from the budget tier is a legitimate option for hobbyists who want to test the TrigJig workflow without investing in a name-brand tool. Its etchings are clean, and the aluminum body is rigid enough for layout work on softwood lumber. That said, the edge tolerances on budget squares are less consistent, so you should verify that the TrigJig clips on evenly before relying on it for production cuts.
Aluminum Alloy Rafter Square Laser-Etched – The Compact Craftsman Tool
The laser-etched red square offers fine detail and a comfortable grip, making it a solid choice for finish carpenters and furniture makers who occasionally need rafter layout. The laser-etched scales are crisp, but the single review count means the long-term durability is unproven. It works with the TrigJig as long as the body profile matches the standard 7-inch geometry, but it is best reserved for light-duty use.
Expert Insights: Fine-Tuning Compound Rafter Layouts
Experienced framers know that the difference between a good rafter joint and a great one is often in the preparation, not just the angle. The TrigJig gets the geometry right, but you still need to control for lumber thickness, saw blade kerf, and the natural variation in dimensional lumber.
Always use a sharp pencil with a fine point or a marking knife when scribing from the TrigJig. A fat carpenter’s pencil adds enough error to shift a compound joint significantly when the rafter is deep. Additionally, hold the square firmly against the lumber face so the accessory does not rotate as you scribe; a cam-locked TrigJig stays put, but the operator’s grip is still part of the equation.
When cutting the rafter, use a blade with a high tooth count and a stable base plate. A dull framing blade will deflect at the entry point, producing a curved cut that defeats the accuracy of the TrigJig layout. For hip and valley jack rafters, many professionals set the circular saw bevel to match the roof pitch angle, but you should confirm this against the joint geometry on a test piece before committing to a full cut.
Common Mistakes to Avoid When Using a TrigJig Accessory
The TrigJig is a simple tool, but it still rewards careful setup. Avoid these recurring mistakes to keep your cuts accurate.
- Setting the TrigJig to the common rafter table value instead of the hip/valley value; this produces a side cut that is too steep and leaves the joint proud.
- Failing to lock the cam after sliding the marker; the accessory drifts during scribing and creates inconsistent angles across multiple rafters.
- Using a speed square with a damaged or rounded back edge; the TrigJig needs a flat reference surface to maintain calibration.
- Marking from the wrong face of the rafter; hip and valley side cuts are mirrored, so always lay out all rafters from the same face orientation.
- Skipping the test cut; compound rafter joints are unforgiving, and a 10-minute test saves hours of re-cutting on the roof.
- Mixing rafter stock thicknesses; the TrigJig setup assumes consistent lumber dimensions, so check that all your stock is the same nominal size.
Frequently Asked Questions
Is the TrigJig compatible with any 7-inch speed square?
The TrigJig is designed around the Swanson-style 7-inch speed square profile, which includes most aluminum rafter squares sold at big-box stores. Genuine Swanson squares such as the S0101 and S0100 provide the most reliable fit because of their consistent edge geometry.
Can the TrigJig be used for common rafter cuts?
Yes, but it offers the most value on compound cuts. For a straight common rafter plumb cut, the speed square alone works perfectly. The TrigJig earns its place when you need a side cut that matches a hip or valley rafter’s diagonal geometry.
What roof pitches does the TrigJig support?
The TrigJig supports the full range of pitches printed in the speed square’s rafter table, typically from 1/12 up to 12/12. The same workflow applies at every pitch; you change the hip/valley rafter value you set on the accessory’s scale.
Final Verdict: The Ultimate Companion for Accurate Rafter Cuts
The TrigJig accessory fills a genuine gap in the speed square system, transforming a simple layout tool into a compound-angle powerhouse. Whether you are framing a full roof, adding a hip dormer, or repairing a valley section on an existing structure, the TrigJig delivers the accuracy you need without requiring a construction calculator or advanced trigonometry knowledge.
The best speed square to pair with it remains the Swanson Speed Square Pro S0100 for professional users, while the Swanson S0101 offers the same core performance at a lower price. If you want maximum layout versatility for the money, the SW1201K Value Pack delivers both a TrigJig-ready 7-inch square and a big 12-inch square for full-width rafter marks. Whichever model you choose, adding the TrigJig to the speed square in your pouch means the next hip, valley, or jack rafter will get a clean, structurally sound cut on the very first pass.