Where the names of joints come from

The name of a tsugite or shiguchi refers to one of four things: a shape made at the end of a member, a part cut away, an attached piece such as a peg, or the place where the joint is used. This article sorts the names that appear on this site, limiting itself to those whose meaning can be confirmed in references. Where a reference gives an account of the origin, the source of that account is named.

Names that refer to a shape: ari and kama

Ari (蟻, "ant") refers to a projection with a widened tip, in the shape of a dovetail (kyubi, 鳩尾), made at the end of a timber. It is fitted into another member so that it cannot be pulled out, and it is used in both tsugite and shiguchi^[1]. On the origin of the name, Marusei Komuten, a builder, gives two accounts: that the trapezoidal shape resembles the face of an ant, and that it resembles an ant's fangs^[2]. Tanaka-gumi explains that it looks like the head of an ant^[3]. The dictionary entry does not describe the origin^[1].

Kama-tsugi (鎌継ぎ), the gooseneck scarf joint, is described in the concise edition of Nihon Kokugo Daijiten as a method in which the upper part of the end face of one member is made to project in the shape of a snake's kamakubi (鎌首) and is fitted into the other member. The dictionary cites Nihon Kenchiku Jii (1906) as its source^[6]. JAANUS describes it as a joint in which a tenon (hozo) with the head and neck in one piece is made on one member, and says it was already in use in the 7th century^[7]. Araki Komuten and oomomok explain that the name comes from the head of the male piece resembling the head of a snake^[4][5]. The two explanations are worded identically.

Names that refer to a part: koshikake, ago and mechigai

According to JAANUS, koshikake (腰掛け) is the basic part of a joint that corresponds to "lap or bench"; it resembles a half-lap (aigaki, 相欠き), but the cut is shallower^[8]. In the koshikake-kama-tsugi (housed gooseneck scarf joint), a hole is cut to about half the thickness of the member, and the remaining half forms a stepped koshikake^[9]. On the origin of the name, Araki Komuten explains that the lower half of the female piece has a projection, and the male piece is fitted on it as if sitting down on it^[10].

Ago (腮, also written 顎) refers to a notch made in a member for a shiguchi, specifically the part cut away on the underside of a member such as a tenon^[11]. According to Digital Daijisen, the watari-ago is a shiguchi in which a groove is cut in the lower end of the upper timber and the two are assembled leaving the middle of the upper end of the lower timber^[12]. Shimizu Corporation states that it is used to join two members that cross horizontally at a right angle, at somewhat different heights^[13].

According to Digital Daijisen, mechigai (目違い) is the part of a tsugite or kumite (組み手) that is set a little way in from the joining point^[25]. The kanawa-tsugi (rabbeted scarf splice with a square peg) is described as a joint in which this mechigai is made in a T shape and the pieces are assembled^[20][21].

Names that refer to an attached piece: pegs and shachi

Shachi (車知) refers to a peg driven in at a slant to the direction of the tenon in order to tighten a joint^[26]. JAANUS gives shachi as an abbreviation of shachi-sen (車知栓), a peg made of hard wood such as keyaki (zelkova) or oak, driven obliquely or at a right angle into the upper and lower parts of a joint^[27]. Marusei Komuten describes a splice in which a shachi-sen is driven into the tenon of a sao (竿, a long rod-shaped neck)^[37] and its mortise to fix them as shachi-tsugi^[29]. A shachi-tsugi is also found in the joints of Japanese wooden boats, where it refers to a joint in which projections and recesses are made in the two members and fitted together^[28]. The same name thus has two uses, one in building and one in boatbuilding.

Names that refer to position or use: daimochi, okkake and kanawa

The daimochi-tsugi (sloped lap splice over a post) is a splice in which the end faces of the two members are cut at a slope and assembled; it is used for round-log roof beams (koyabari, 小屋梁) and similar members^[14][17]. Araki Komuten explains that dowels are driven through the joining surface and that the joint is fixed by the load on it, for example from a tsuka (束) standing on the joint^[16]. In Araki Komuten's explanation, the splice is made at the top of a post^[16]. When it is worked in a round log, the cut face takes the shape of a choshi (銚子), so it is also called choshi-tsugi (銚子継ぎ)^[14][15][16].

The okkake-daisen-tsugi (sloped scarf splice with square pegs) is a splice for large members such as eaves girders (nokigeta, 軒桁). It is a half-lap (aigaki) with an ago and an eriwa (襟輪), fixed with a komisen (a square peg). The version without a komisen is called okkake-tsugi to distinguish it. On site it is often simply called okkake^[23].

According to the Japanese Wikipedia, the kanawa-tsugi is a joint in which a T-shaped mechigai is made in the ends of two pieces of the same shape, and a peg is inserted to fix them^[20]. It is used for netsugi (repairing the foot of a post) and for parts where bending occurs, such as girders^[18]. On the origin of the name, a blog by Minka Kobo relays two accounts: that the joint is stronger than a timber bound with an iron ring, and that it is so strong that the pieces would never come apart, in the sense of the phrase konrinzai (金輪際). The blog does not say whose accounts these are^[22]. The dictionary entry for kanawa (金輪) lists, among other meanings, the chirin (地輪) of Buddhism, which lies above the suirin (水輪) and supports the kuzan-hakkai (九山八海), and an iron stand placed on a hibachi or irori hearth^[19].

The "dai" (大) of daisen, the "dai" (台) of daimochi, the origin of okkake, the "watari" (渡り) of watari-ago, and the etymology of shachi were not described in the dictionaries and explanations that were checked.

Variant spellings

Ooire (大入れ), housing, is one kind of shiguchi in timber construction in which the whole end of one member is inserted into another. It is also called oire (尾入れ)^[30]. It is also written 追入れ (read oi or ooire), and it joins members at a right angle without showing the end face of the timber^[31][32]. This site uses 大入れ (Ooire).

Okurigana, the kana that follow a kanji, vary between sources. "金輪継ぎ" and "金輪継" ^[18][20], "鎌継ぎ" and "鎌継" ^[4][5][7], and "追掛け（大栓継）" and "追掛大栓継" ^[23][24] each refer to the same joint.

See them in 3D

On the screens of this site, these names are shown with their readings. For example, the okkake-daisen-tsugi is read おっかけだいせんつぎ, the kanawa-tsugi かなわつぎ, and the watari-ago わたりあご.

• Ari and koshikake: Ari-tsugi, Koshikake-ari-tsugi, Koshikake-kama-tsugi
• Daimochi, okkake and kanawa: Daimochi-tsugi, Okkake-daisen-tsugi, Kanawa-tsugi
• Ago, ooire and shachi: Watari-ago, Ooire-ari-kake, Sao-shachi-tsugi
• All joints