Zouma Xiao (走马销): The Sliding Key Joint

Zouma xiao · 栽榫 (planted tenon) · 挂楔

A Ming couch bed has heavy railings on three sides, yet it can be lifted apart and moved. No screws, no glue at the railings. The secret is a small block of wood with a big name.

The zouma xiao, literally “galloping-horse key”, is a dovetailed pin that drops into a slot and slides to lock. Slide it back, and the parts come away.

Chinese: 走马销 · zǒumǎ xiāo
Also called: 栽榫, 桩头, 挂楔
Joins: Parts that must come apart
Found in: Couch-bed railings, screens, thick board panels
Signature parts: Separate pin · wide-and-narrow mortise

Drag to rotate. Slide to take the joint apart, or press Assemble to watch it go together.

How it works

A planted pin

Parts that are taken apart wear their tenons. So the pin is made of a separate piece of wood and planted into one member. If it wears or breaks, you replace the pin, not the whole railing.

Wide end, narrow end

The pin is narrow at its root and wide at its tip. The mortise in the other member is wide at one end and narrow at the other. Drop the pin into the wide end, push the part along, and the pin’s wide tip slides under the narrow end. It can no longer be lifted out.

Taking it apart

Knock the part back the other way, the pin returns to the wide end, and it lifts free.

How it's made

Step 1
Plant the pin
Make the pin from a separate piece of hard wood and plant it in one member.
Step 2
Shape the pin
It is narrow at the root and wide at the tip.
Step 3
Cut the slot
Cut a mortise in the other member, wide at one end and narrow at the other.
Step 4
Drop it in
Lower the pin into the wide end of the slot.
Step 5
Slide to lock
Push the part along so the pin moves into the narrow end.
Step 6
Take it apart
To dismantle, slide it back and lift.

Variations

Couch-bed railings

The classic place: between the railings, and between the side railings and the bed frame.

Board joints

Thick boards can be joined edge to edge with zouma pins.

Can you CNC this?

Possible, with design or setup changes

The keyhole slot is undercut, so it needs a dovetail or T-slot cutter on a 3-axis machine: plunge at the wide end, then run to the narrow end. The dovetailed key can be cut with the same bit. Expect to tune the fit.

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)

Lower part with slot 带销槽的下件 · zouma-xiao-lower-part.stl
Upper part with key 带走马销的上件 · zouma-xiao-upper-part.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).