Two families: tsugite and shiguchi
JAANUS gives the division plainly: tsugite join timbers end to end to increase their length; shiguchi join them at an angle. A tsugite has to carry a beam or sill across a joint as if it were one piece, so where it sits matters — JAANUS distinguishes a joint set directly over a supporting post from one that overhangs the support, which it notes is weaker. Even which end of the tree each timber came from is considered: ends from the top of the trunk, from its base, or one of each are joined in named ways. A shiguchi, by contrast, connects a beam to a post, a sill to a corner pillar or one member across another, and is built mostly from tenons, laps and dovetail shapes.
| Term | Meaning | Family |
|---|---|---|
| Tsugite 継手 | A joint that lengthens timbers end to end | — |
| Shiguchi 仕口 | A joint at an angle | — |
| Hozo ほぞ | A tenon; the mortise is hozoana | Both |
| Ari 蟻 | Any dovetail-shaped part of a joint | Both |
| Koshikake 腰掛 | A shallow lap or 'bench' within a joint | Both |
| Kamatsugi 鎌継 | A gooseneck splice: a head on a neck, set into a matching mortise | Tsugite |
| Kanawatsugi 金輪継 | A blind, stepped scarf, slid together lengthwise and locked by a draw pin or keys | Tsugite |
| Aigaki 相欠 | A corner lap without a mitre | Shiguchi |
| Sen 栓 and shachi 車知 | A wooden pin and a long key that lock a joint | Both |
Definitions from JAANUS, paraphrased. JAANUS also lists double and quadruple tenons, the wedged 'fox' tenon and many more.
Locked by shape, pins and keys
Many Japanese joints hold because their parts cannot slide apart in the directions the structure loads them, and are then locked with wood. Kanawatsugi is the example JAANUS gives: both halves are blind, so the joint cannot be slipped together from the side; it is slid together lengthwise and locked by a draw pin driven through the middle, or by two keys. JAANUS ties joints of this complexity to the better carpenter's tools of the Edo period. The dovetail has a long history too: JAANUS dates the earliest known dovetailed splices to the bracket arms of Daigoji's five-storied pagoda, of 952, and says dovetails were made longer and narrower, and combined with other joints, from the 14th century. The Western dovetail family is in dovetail joints; tenons and their variants in mortise and tenon joints.
Where the tradition lives
Most of these joints come from building — temples, shrines, houses — and the skills to make and repair them are recognised by UNESCO, which inscribed Japan's traditional skills, techniques and knowledge for conserving and transmitting wooden architecture on its Representative List in 2020. Japan's nomination describes knowledge passed from master craftspeople to apprentices, preservation associations formed as modernisation made that harder, and Horyu-ji, built in the early 7th century, as the oldest surviving wooden structure. In furniture and fittings the same thinking appears at a smaller scale, and in the lattice craft of kumiko.
- Tools: Japanese pull saws cut on the pull stroke — see Japanese saws — and the chisels and planes are in chisels and hand planes.
- A first project: the corner laps and half-lapped crossings of a kumiko lattice panel are a practical start.
- Choosing a joint generally: see choosing a wood joint.
Reading a Japanese joint
- End to end (tsugite) or at an angle (shiguchi)
- Which basic parts it is made from: tenon, lap, dovetail, scarf
- How it is assembled: dropped in, slid lengthwise, or knocked across
- What locks it: its own shape, a pin (sen) or a key (shachi)
- For a tsugite, whether it sits over a support
- The name, which usually describes the parts
Sources
Terms and definitions are JAANUS's, paraphrased; JAANUS gives many more variants than are listed here. No source reviewed says that Japanese joinery never uses metal fasteners, so the page says only what the sources show: joints locked by their own shapes and by wooden pins and keys.
- 1.
tsugite 継手 (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Tsugite as joints that lengthen timbers end to end, set against shiguchi as angle joints; the three ways ends from the top and base of the trunk are paired; a joint set over a support as against one that overhangs it, which is weaker; and the four basic methods — tenon and mortise, lap, splint and scarf.
- 2.
shiguchi 仕口 (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Shiguchi in two groups — crossed or angled timbers (T-joints, half-lapped dovetails, cogged laps, mitres, corner laps) and assemblies of tenons and mortises — often reinforced by pins (sen) or long keys (shachi).
- 3.
hozo ほぞ (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Hozo, the tenon, and its many forms — single, double and quadruple, haunched, stacked, three-pronged, dovetail and wedged tenons.
- 4.
ari 蟻 (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Ari, any dovetail-shaped part of a joint; the earliest known dovetailed splices on the bracket arms of the five-storied pagoda at Daigoji (952); dovetails made longer and narrower, and combined with other joints, from the 14th century; rounded, half, lapped and blind forms.
- 5.
kamatsugi 鎌継 (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Kamatsugi, the gooseneck splice, used as early as the 7th century, usually to join two beams.
- 6.
kanawatsugi 金輪継 (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Kanawatsugi, a complex blind scarf assembled lengthwise and locked by a draw pin or two keys, used in sills, wall plates and eave purlins, and made possible by the better tools of the Edo period.
- 7.
koshikake 腰掛 (glossary entry). Japanese Architecture and Art Net Users System (JAANUS).
Used for: Koshikake, the shallow lap or 'bench' that forms part of many joints.
- 8.
Traditional skills, techniques and knowledge for the conservation and transmission of wooden architecture in Japan. UNESCO Intangible Cultural Heritage.
Used for: The inscription of Japan's traditional skills for conserving and transmitting wooden architecture on UNESCO's Representative List in 2020, and its extension in 2025.
- 9.
Nomination file No. 01618 for inscription in 2020 (Form ICH-02). UNESCO Intangible Cultural Heritage / Government of Japan, 2019.
Used for: Knowledge passed from master craftspeople to apprentices, preservation associations formed as modernisation made that harder, and Horyu-ji, built in the early 7th century, as the oldest surviving wooden structure.
About this reference
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