Figure-4 Trigger

Part of Hunting and Trapping

The figure-4 is the most widely used deadfall trigger in the world — three sticks, three notches, no cordage required. It has been used for thousands of years because it works.

Why the Figure-4

The figure-4 trigger earns its name from the shape the three assembled sticks form — they interlock to create a shape resembling the numeral “4.” The design is elegant: each stick supports the others in a self-locking geometry that can hold significant weight but collapses instantly when the bait stick is disturbed.

No cordage. No metal. No manufactured parts. Three sticks and a cutting tool are all you need. This makes it the most universally buildable trap trigger in any environment where wood exists.

The Three Components

Each stick has a specific name and function. Understanding what each one does prevents errors during carving and assembly.

Component	Also Called	Function	Typical Length
Upright	Vertical stick, post	Stands vertically, holds the diagonal	15-25 cm
Diagonal	Support stick, lever	Angles from upright to weight, bears the load	20-35 cm
Bait stick	Horizontal, trigger	Extends horizontally under the weight, holds bait	20-30 cm

All three sticks should be cut from dead, dry hardwood — green wood compresses under load and soft wood crumbles at the notches. Oak, maple, ash, hickory, and beech are excellent. Avoid pine, willow, and poplar — too soft for reliable notch engagement.

Stick diameter should be roughly 1-2 cm (pencil to thumb thickness) for small game triggers, and 2-4 cm for larger weights targeting rabbits or raccoons.

Carving the Notches

This is where most beginners fail. The notches must be precise enough to interlock securely but shallow enough to release under light force. Each stick requires specific cuts.

The Upright Stick

Step 1. Cut a flat base at the bottom so it stands vertically on hard ground without wobbling. If the surface is soft, stand it on a small flat stone.

Step 2. Near the top (2-3 cm from the end), carve a square notch on one side. This notch faces the direction the diagonal stick will come from. Cut it flat and perpendicular to the stick — approximately half the diameter deep.

Step 3. At the very top, carve the end to a chisel point or flat shelf. This is where the diagonal stick rests.

The Diagonal Stick

Step 4. At the upper end (the end that will touch the upright), carve a matching square notch that interlocks with the upright’s notch. These two notches fit together at a right angle — like two puzzle pieces. When assembled, the diagonal extends upward from the upright at roughly 45 degrees.

Step 5. At the lower end (the end that goes under the weight), carve the tip to a blunt chisel point. This point presses against the underside of the weight and provides the support surface.

Step 6. Midway along the diagonal, on the underside, carve a small notch or groove — this is where the bait stick will engage. The notch should be just deep enough to hold the bait stick’s end securely but shallow enough that a slight upward or lateral force from the bait stick will disengage it.

The Bait Stick

Step 7. At one end, carve a flat chisel edge that engages with the notch on the underside of the diagonal. The angle of this chisel determines how sensitive the trigger is:

• More perpendicular (closer to 90 degrees): Less sensitive — animal must pull harder
• More angled (closer to 45 degrees): More sensitive — light touch releases

Step 8. At the opposite end, carve a small notch or point to hold the bait. You can also simply sharpen the tip and skewer the bait onto it.

Step 9. Near the bait end, on the underside, carve a square notch that matches the upright stick’s top. This is where the bait stick rests on top of the upright, completing the “4” shape.

Notch Depth

The most common error is cutting notches too deep. Deep notches create a stable, strong joint — which is exactly what you do not want. The trigger should hold the weight securely but release with approximately 50-100 grams of lateral force on the bait. Start shallow. You can always deepen a notch, but you cannot undo an over-cut.

Assembly

Step 10: Dry Assembly (No Weight)

Practice assembly without the deadfall weight first:

1. Stand the upright vertically on hard ground or a flat stone
2. Place the bait stick horizontally, resting its notch on top of the upright
3. Set the diagonal at roughly 45 degrees, interlocking its upper notch with the upright’s notch, and engaging its mid-point notch with the bait stick’s chisel end

The three sticks should hold each other in place through interlocking geometry. If assembled correctly:

• The upright stands vertical
• The bait stick extends horizontal, with bait on the far end
• The diagonal extends at 45 degrees from the upright to the point where the weight will be
• Viewed from the side, the shape clearly resembles “4”

Step 11: Load the Weight

This is the dangerous step. The weight must be heavy enough to kill the target animal.

1. Tilt the weight (stone or log) up on edge beside the assembled trigger
2. Carefully slide the tip of the diagonal stick under the weight, supporting it
3. Slowly lower the weight onto the diagonal’s tip until the trigger assembly bears the full load
4. Remove your hands gently — do not bump any component

If the trigger collapses during loading, the weight falls harmlessly to the side (it should not fall toward you). Reset and try again. Common causes of collapse during loading:

• Notches too shallow (deepen slightly)
• Weight placed too far from the upright (shorten the distance)
• Upright on soft ground (place on flat stone)

Step 12: Sensitivity Test

Use a long twig (50+ cm) to gently push the bait from the direction the animal will approach:

• Too stiff: Shave the bait stick’s chisel end to a more acute angle, or shave the diagonal’s engagement notch slightly shallower
• Too sensitive: Deepen the engagement notch slightly, or make the bait stick’s chisel more perpendicular
• Just right: The trigger releases with a light pull on the bait, and the weight falls flat onto the kill zone

Test three times. If it fires reliably all three times, it is ready.

Scaling the Trigger

The figure-4 scales from mouse-weight traps to 50+ kg deadfalls. Adjust stick dimensions proportionally:

Target Weight Range	Stick Diameter	Stick Lengths	Notch Depth
Under 1 kg	5-8 mm	8-15 cm	2-3 mm
1-5 kg	8-12 mm	12-20 cm	3-5 mm
5-15 kg	12-18 mm	18-25 cm	5-8 mm
15-30 kg	18-25 mm	22-30 cm	6-10 mm
30-50+ kg	25-40 mm	28-40 cm	8-12 mm

For very heavy weights, consider doubling the upright or using thicker, stronger wood. The diagonal bears the most stress — select the straightest, hardest stick for this component.

Troubleshooting

Problem	Cause	Fix
Weight slides off diagonal tip	Tip too pointed or smooth	Carve a broader, flatter tip; roughen surface
Diagonal rotates sideways	Upper notch engagement too loose	Deepen the interlocking notch on one side
Bait stick falls out during setup	Chisel edge too acute or notch too shallow	Adjust engagement angle; slightly deepen diagonal notch
Trigger fires from wind	Overall sensitivity too high	Deepen engagement notches by 1 mm increments
Animal takes bait without triggering	Trigger too stiff	Shave engagement surfaces thinner; reduce notch depth
Upright tilts and collapses	Soft ground or uneven base	Stand on flat stone; cut flat base

Practice Protocol

Do not attempt your first figure-4 in a survival situation. Practice now.

Step 13. Gather materials and build 5 triggers in succession. Time yourself:

• First attempt: 15-30 minutes (normal)
• By fifth attempt: 5-10 minutes (target)
• Expert level: under 3 minutes

Step 14. Test each with a weight. A book or a brick works for practice. Drop-test at least 3 times per trigger. Aim for 100% fire rate.

Step 15. Build triggers in different wood species. Learn what carves well and what crumbles. Learn the grain direction of each species — always carve with the grain on load-bearing surfaces, never across it.

Common Mistakes

• Using green or soft wood. The notches compress under load, the trigger slowly settles, and the weight either falls on its own or the trigger becomes too stiff to fire. Use dead, dry hardwood only.
• Making all notches the same depth. Each notch serves a different function. The load-bearing notch (upright-to-diagonal) should be firm. The trigger notch (diagonal-to-bait stick) should be shallow and easy to release. Match depth to function.
• Not testing sensitivity. Every figure-4 you build should be tested with a long stick before you leave it. An untested trigger has unknown behavior — it might be too stiff or too loose.
• Carving against the grain on the diagonal. The diagonal bears the entire weight. Cross-grain notches crack under load, splitting the stick and collapsing the trap spontaneously.
• Rushing the carving. Precise notches take 5-10 minutes of careful work. Rough, imprecise cuts create unpredictable engagement. The time invested in clean carving pays back in reliable triggering.

Key Takeaways

• The figure-4 uses three sticks with interlocking notches — upright (vertical), diagonal (load-bearing), and bait stick (horizontal trigger)
• Use dead, dry hardwood; avoid softwoods that compress under load
• The trigger notch (diagonal-to-bait stick) must be the shallowest — it determines sensitivity
• Always test the assembled trigger three times with a long twig before leaving; adjust notch depth until it fires reliably with light force
• Carve with the grain on all load-bearing notches; cross-grain cuts split under weight
• Practice building figure-4 triggers before you need one — target under 10 minutes from raw sticks to loaded, tested trap