Gougua Sun (勾挂榫): The Hooked, Wedged Tenon
Hook tenon · 勾挂垫榫
Some Chinese braces have to lock into a leg from one side only, with no way to pin them from outside.
The answer is a tenon that hooks: put in low, pushed up, and wedged so it can never drop back.
- Chinese
- 勾挂榫 · gōuguà sǔn
- Also called
- 勾挂垫榫
- Joins
- Brace or stretcher to leg
- Found in
- The lower end of the bawang brace
- Signature parts
- Right-trapezoid tenon · taller mortise · wedge
How it works
A trapezoid tenon
The tenon and the mortise are both shaped as right trapezoids. The mortise is taller than the tenon root.
In low, push up
Wang Shixiang describes the bawang brace’s lower end: the tenon goes into the wider lower part of the mortise and is pushed up into the narrower upper part, where the sloping faces bear on each other and hook.
Wedge
A wedge is driven into the space left below, so the tenon cannot drop and therefore cannot come out.
How it's made
Step 1Trapezoid tenon
Shape the tenon as a right trapezoid.
Step 2Taller mortise
Cut a mortise taller than the tenon root.
Step 3In low, push up
Insert low, then push up.
Step 4Hooked
The sloping faces hook together.
Step 5Wedge
Drive a wedge into the gap below.
Step 6Locked
It can no longer pull out.
Variations
Bawang brace
The best-known use, at the brace’s lower end.
Can you CNC this?
Hard on a 3-axis machine as drawn
Hard as drawn: the hook relies on sloping faces inside the mortise, which a straight cutter entering from the face cannot reach. A version with a straight hook and a dovetail-bit undercut may work, but it would need testing.
General note: a round cutter cannot leave a sharp inside corner, so every recess keeps the tool radius. Round the mating edges or add dogbone reliefs. Sloping faces, undercuts and curves may need special bits, extra setups or more axes.
Free STL downloads (one file per part)
- Leg 腿足 · gougua-sun-leg.stl
- Brace with hooked tenon 带勾挂榫的枨子 · gougua-sun-brace.stl
- Wedge 楔子 · gougua-sun-wedge.stl
Proportions are illustrative, not measured dimensions. The files are unitless: scale them to suit and check fits and allowances before cutting. Each file is a closed (watertight) solid with its mortises and slots already cut, exported in its assembled position, ready to import into CAM or modelling software. Licence: CC BY 4.0 (credit: Chinese Joinery).
Related joints
Questions
What is a gougua tenon?
A trapezoid tenon that hooks in a taller mortise and is locked by a wedge below.
Where is it used?
Most famously at the lower end of the bawang brace.
Can it be taken apart?
Only by removing the wedge first.