Graduated rule
The hardened rule has photo-engraved markings. Read from the chosen edge and use the same face of the stock for repeated layout.
Hand Tools / Layout Tools / Field guide
Combination Square
Use one sliding rule and two clean reference faces to measure, mark square and transfer a 45-degree line.
12 inRule90° + 45°Faces
01 / Tool anatomy
See the assembled tool and its components
An original educational poster identifies 8 documented construction features. The numbered descriptions remain readable below the artwork on narrow screens.
- Steel rule
Slides through the head; reversible blade supplies the straight measuring edge.
- Graduated edge
Photo-engraved graduations support measurement and repeatable layout.
- Square head
Cast-iron head holds the rule and establishes the reference faces.
- 90° reference face
Long outside bearing face supports square layout from an edge.
- 45° reference face
Angled shoulder supports miter layout when seated cleanly.
- Rule lock
Knurled nut and bolt secure the selected blade position.
- Spirit vial
Built-in vial offers a level reference within the head.
- Stored scriber
Removable pointed scriber is stored in the head for layout marks.
Technical references: Starrett C11H-12-4R official product · Starrett combination-square instructions. The rule slides through the square head and can be reversed. The lock, vial and stored scriber are features of the head; this arrangement is educational, not a service disassembly. Original educational artwork depicts documented component groups and their relationships; it is not a service sequence or a replacement for the exact model manual.
02 / Understand the tool
What it is and what each part does
The Starrett C11H-12-4R is a two-piece combination square: a 12-inch satin-chrome graduated steel rule slides through a black cast-iron square head. The head also carries a spirit vial and stored scriber. This selected model does not include the optional center or protractor heads offered in other combination-square sets. A dedicated engineer's square is simpler for a single fixed 90-degree check; the sliding rule adds repeatable offsets and depth readings.
The rule's longitudinal groove engages a reversible lock bolt in the head. Loosen the knurled nut to slide or withdraw the rule, seat it fully against its bearing surfaces, then tighten without forcing it. The two machined head faces reference 90 and 45 degrees to a clean work edge. The educational construction view withdraws only the rule; it does not propose removing the vial or dismantling the head.
Square head
The cast-iron head carries the blade channel and machined 90- and 45-degree reference faces. Chips between head and wood spoil accuracy.
Blade lock
The knurled nut and bolt hold the rule at a chosen projection. The blade can be reversed or withdrawn as the official instructions describe.
Vial and scriber
A built-in spirit vial gives a rough level reference. The removable scriber stores in the head; it is a marking aid, not a cutting blade.
01 / Working relationship
How the main groups connect
02 / Working setup
Keep the head on one reference edge
02 / Working principle
Set, guide and control the action
These decisions make the mechanism useful at the bench.
Check the reference
Wipe the head face and board edge, then inspect for burrs before relying on a line.
Set the projection
Loosen the lock, set the rule to the intended offset, fully seat it in the head and tighten gently.
Transfer a line
Keep the selected head face against a known straight edge and draw a fine line with a pencil or the stored scriber.
Square and miter layout
Mark crosscuts at 90 degrees or miters at 45 degrees from a prepared reference edge.
Depth and offset
Slide the rule to read a recess depth or transfer a repeated distance from a board edge.
Machine setup
With a machine off and safe, compare blade or fence offsets using a common rule datum and appropriate guarding.
03 / At the bench
Setup, technique and finish quality
Use the steps for a first pass, then inspect the work before changing the setup.
- Inspect the rule, head, blade channel and reference faces for damage or debris.
- Mark a reference face and edge on the work; check that the edge is straight.
- Loosen the head lock, slide the rule to the desired projection and tighten gently.
- Seat the 90-degree or 45-degree head face firmly against the reference edge.
- Mark with a fine pencil or the stored scriber without letting the head rock.
- Verify a critical square setting by drawing a line, reversing the head against the same straight edge and comparing the lines.
The datum is the head face
A precision scale cannot rescue layout taken from a rough edge or a head lifted by sawdust.
Reversal exposes error
Comparing lines from opposite orientations reveals head or seating error without assuming the printed graduation is perfect.
One selected configuration
The poster depicts the C11H square head and rule. Optional protractor and center heads are other configurations, not hidden parts.
What changes by model or material
Choose a blade long enough for the work and a graduation pattern readable for the chosen unit system.
Cast-iron, forged and die-cast heads differ in durability and cost; verify the actual model's accuracy.
Center and protractor heads expand tasks but require their own handling and calibration checks.
Choosing the tool
- Look for flat, burr-free 90- and 45-degree faces and a rule that locks without twist.
- Pick a rule length and graduation pattern suited to your usual layout.
- Check maker support for replacement rules and lock hardware.
Useful accessories
- Fine marking pencil or knife
- Reference straightedge
- Protective case
Consumables
- Light corrosion protection for the steel rule
04 / Keep control
Care, troubleshooting and safety
Secure the work, protect sharp edges and release any stored clamping pressure before adjustment or maintenance.
Care checklist
- Wipe the rule and head after use.
- Keep grit out of the blade channel and off the machined faces.
- Store the rule secured without overtightening the lock.
- Check square after a drop; repair or replace a damaged head.
Common mistakes
- Reading from the wrong rule edge.
- Marking from an unprepared board edge.
- Tightening while the rule is tilted in its channel.
- Using the vial as a substitute for a precise level.
Safety at the operation
- Keep the steel scriber capped or stored when not in use.
- Keep hands away from a machine cutter during setup and disconnect power where the machine instructions require.
- Do not use a bent rule or damaged head for critical layout.
When the result goes wrong
Clean the head and reference edge, reseat the rule, then inspect the head for damage or lost square.
Inspect groove, lock bolt and nut for debris or wear; use the maker's replacement parts.
Confirm the reading edge, unit scale and rule orientation before remarking the work.
05 / Sources to keep learning
Manuals and educational resources
Use the exact model documentation for setup, limits and replacement parts. These lessons, documents and model pages teach relevant techniques or help compare real variations.
Manufacturer documentation
Learn and compare
06 / Manufacturer directory
Manufacturers & Brands
These maker-owned links document relevant tools and tool brands. A product brand may use another company's factory; compare the exact model before choosing parts or accessories.
Choose parts for the exact model
Handles, irons, saw plates, clamping pads and other replacements vary by maker and model. Use the maker's documentation before changing a component.
Compare the Layout Tools family →Continue through the Tools library