Mekugi-Ana Drilling and Nakago Finishing: The Precision Craft of Joining Blade to Handle in Japanese Sword Making

What is a Mekugi Hole? — The Small Hole Connecting Blade and Handle

A "mekugi hole" is a small opening made in the nakago (the tang—the part of the blade that is inserted into the handle) of a Japanese sword. After inserting the nakago into the handle (tsuka), a thin pin called a "mekugi" (typically made of bamboo) is driven through from the side of the handle to secure it. As long as the mekugi remains in place, the nakago cannot become separated from the handle.

This small hole actually holds tremendous importance in determining the sword's function, safety, and historical provenance.

Mekugi Materials and Role — Why Bamboo?

The most common material for mekugi is "bamboo" (take). Metal mekugi do exist (primarily for ceremonial and decorative purposes), but practical swords rely on bamboo pins as standard.

Bamboo is chosen as the mekugi material for the following reasons.

Appropriate hardness and elasticity: Bamboo is hard and resistant to breaking, yet possesses enough flexibility to absorb impact.

Easy sourcing and replacement: Bamboo could be obtained readily even during campaigns or distant expeditions, allowing for field replacement if a mekugi broke.

Safety valve function: When excessive impact occurs (such as the blade striking an object), the bamboo mekugi breaks first, functioning as a "fuse" that minimizes damage to the nakago and handle.

Mekugi Hole Positioning — A Critical Decision by the Smith

The position of the mekugi hole is determined by the sword smith during the final finishing stage of the nakago. Positioning requires the following considerations.

Nakago Strength and Hole Position

Since the mekugi hole pierces through the nakago, it must be placed where it does not compromise the strength of the tang.

Basic principle: The hole is placed at the center of the nakago (the middle of the tang width). Off-center positioning makes the tang prone to breakage.

Vertical positioning: The hole is typically placed at a set distance (usually 5-8 cm) from the machi (the boundary between nakago and blade). This distance varies according to the sword's purpose (practical or ceremonial), era, and school.

Alignment with handle length: The length of the handle must align with the length of the nakago and the position of the mekugi hole. Otherwise, the handle will not fit properly on the nakago. Smiths often consulted with handle makers to determine the optimal position.

Historical Trends — Positional Changes Over Time

The position of the mekugi hole on the nakago exhibits historical tendencies. In general, older swords (Kamakura and Nanboku-chō periods) tend to have holes positioned closer to the machi (near the root of the tang), while newer swords (Edo period) tend to have holes positioned slightly farther (toward the middle of the tang). However, this is a general trend; individual schools and smiths showed considerable variation.

Mekugi Hole Drilling Technique — How the Hole is Made

Drilling the mekugi hole is one of the final stages in nakago finishing.

Tools Used

Mekugi-kiri (mekugi drill): A specialized drill designed specifically for mekugi holes. Unlike ordinary drills, specialized tools matching the desired hole shape (circular or angular) are employed.

Drilling procedure

1. The position of the mekugi hole on the nakago is marked with ink (sumi) or a chisel (tagane)
2. The mekugi-kiri is used to drill gradually (the tang steel becomes harder after heat treatment, requiring careful work)
3. The edges (burrs) of the hole are carefully removed, finishing the hole so the mekugi passes through smoothly

Hole Shape — Square and Round Holes

The cross-sectional shape of the mekugi hole comes in two types: "square holes" (kaku-ana) and "round holes" (maru-ana).

Square holes (rectangular cross-section): Bamboo mekugi are often shaped with a square cross-section, and matching square holes represent the traditional form. Square holes prevent the mekugi from rotating, providing stable fixation.

Round holes (circular cross-section): A more modern form, more commonly used when employing metal mekugi (rivets or pins). Modern swords and iaido practice swords sometimes feature round holes.

From an authentication perspective, the shape, size, and finishing quality of the hole serve as material for estimating the era and school of the sword.

The Significance of Multiple Mekugi Holes — Evidence of Shortening

When a nakago has multiple mekugi holes, each hole carries different significance.

Evidence of Shortening (Suriage)

The most important case is "shortening" (suriage). When a longer tachi is cut short and converted into a katana or wakizashi, the original mekugi hole position changes, necessitating a new hole.

The old hole from before shortening may remain as an "old hole" (ume-ana) or remain near the new hole. From these multiple holes, one can determine that "this sword underwent shortening."

Significance in authentication: Because shortening reduces the length of the nakago, the original smith's signature (mei) may have been cut away. Many swords authenticated as "unsigned" (mumei) have lost their signatures due to shortening.

Evidence of Handle Repair or Replacement

When a handle is replaced and the original mekugi hole no longer aligns, a new hole is drilled, resulting in multiple holes.

Application to Provenance Estimation

The number, position, and shape of mekugi holes are important elements in "reading the nakago." Skilled authenticators can infer the following from mekugi holes:

• Whether shortening occurred and when
• How many times the handle was replaced
• The size of the handles that were used (the position where it was secured)

Precision Finishing of the Nakago — File Marks, Machi, and Shape

Alongside the mekugi hole work, the overall finishing of the nakago embodies the sword smith's technical mastery.

File Marks (Yasuri-me)

The marks left on the nakago surface by filing (yasuri). File marks are not mere finishing but serve the following functions and purposes.

Anti-slip function: When the nakago is inserted into the handle, the irregularities of the file marks create friction, preventing the nakago from sliding within the handle.

School and era characteristics: The pattern of file marks (horizontal files, diagonal files, large sectional files, finishing files, etc.) exhibits distinctive patterns by school and serve as authentication material.

Machi (Boundary) Shape

The machi is the boundary between the nakago and blade, with two locations: the edge machi (ha-machi) and spine machi (mune-machi). The shape of the machi (angle, depth, and finishing precision) is an important authentication point.

Nakago Shape

The shape of the nakago itself (round tang, sword-shaped tang, shallow onion tang, boat-bottomed tang, etc.) also indicates school and era characteristics.

Conclusion — The Mekugi Hole is a Small but Important "Window of Information"

A mekugi hole is only a few millimeters in diameter, yet the technical and historical information embedded within it is vast.

The sword smith incorporates into the mekugi hole's position and shape the sword's intended purpose, the demands of the era, and alignment with the handle. The authenticator reads from the mekugi hole evidence of shortening, modification, and usage history. The enthusiast recognizes that multiple holes represent the time that "this sword has lived through."

If you have the opportunity to hold a Japanese sword, please observe the mekugi hole in the nakago. Within that small hole lies the entire lifespan of the sword, spanning several hundred years.