Hamaguri-ba (蛤刃) Cross-Section

Reference sectionHamaguri-ba (蛤刃)—Clam-Shell Cross-Section

Hamaguri-ba (蛤刃) is Japanese maker terminology for a rounded, convex blade or edge profile that keeps supporting thickness behind a fine edge. The outer face curves outward while the inner face carries a separate hollow, and exact curvature, inner relief and edge treatment are maker- and model-specific. The name does not fix a radius, an angle, a grinding sequence or a cutting result.

Quick look

• Profile: The outer face is convex. On the documented Japanese models the inner face is hollow-ground (urasuki), so the two faces are not the same shape; the exact inner relief is maker- and model-specific. The name comes from the hamaguri (蛤, clam) shell.^1,2
• Origin: Hikari describes the convex profile as drawing on traditional Japanese sword (日本刀) and kitchen-knife geometry, and states that it obtained Japan’s first patent for the blade-angle and polishing method.³

Why it matters

Hamaguri-ba is common in Japanese professional shears, and makers describe it as a soft, smooth cutting construction. Because the outer face curves outward and the inner face is hollowed, the two blades meet along a narrow contact band rather than across their full width, which is what makers and suppliers say gives the section its low-friction release.^1,2

Hikari describes its convex construction as keeping supporting thickness behind the edge rather than a thin grind. How long the edge lasts still depends on the steel, hardness, edge angle and care.³

DetailMaker vocabulary and evidence limits

Hamaguri-ba is maker vocabulary for a rounded, clam-shell-like profile, not a dimensional specification. The name alone does not settle a fixed radius, edge angle, grinding-stage count, abrasive sequence, inner relief, edge finish, cutting result, service interval, or country-specific sharpening method.

• KASHO publishes named models with convex outer surfaces and hollow-ground inner faces. That combination is documented for those models; it does not prove that every shear sold as hamaguri has the same inner relief.
• Naruto contrasts its clam blade with a thicker sword-shaped blade and gives each a different cutting feel. That documents Naruto’s own range, not an industry ranking.

Inner relief, hollow grinding, final honing, and partner-blade construction are separate fields from the section name. So is the plan-view blade line: a straight or willow line may carry its own section and edge description, and hamaguri wording should not be collapsed into it.

No shared technical threshold was found that makes a “clam-shaped” or clamshell edge deeper, more symmetrical, or categorically different from every other convex construction. Treat the translated label as a pointer to the family, then verify the exact model.

Process routeTechnique map

• Slide cutting: Commonly paired with a convex section, because a smooth rounded surface moves through hair with less deliberate grip than a micro-serrated edge.^1,2
• Point cutting: Entry depends on the model’s tip profile, edge and alignment, not on the section name.¹
• Dry cutting: Makers position some convex models for dry and motion cutting; verify the exact model’s stated use.²
• Blunt cutting: Makers position thicker sections, such as ken-ba and sword forms, for heavier cutting. Check the exact model and its stated use.¹

Usage notes

1. Hamaguri-ba edges need a sharpener who can keep the original curve. Hikari warns that unsuitable machine or self-taught grinding can damage its convex edges.³
2. Set tension to the maker’s specification and check it regularly, since loose tension shows up as blade movement on any section.²
3. Clean and oil the interior faces regularly; product build-up on the bearing surfaces works against a smooth close.³

Care and serviceMaintenance

• Return to the manufacturer or a provider qualified for the exact convex geometry. Maker service is one route that preserves the original profile; ask any provider how they will identify and keep it.³
• The inner face is deliberately hollow (urasuki), so never flat-hone the ura side: a flat stone there destroys the hollow. Take any routine for the outer face from the maker.
• Store closed and in a case; the polished convex outer face is vulnerable to nicks from contact with hard surfaces.²
• Before service, record the maker, exact model, blade pair, outer profile, inner relief, edge finish, and service history, and ask the provider how the original geometry will be preserved.

DetailOrigin: Hikari Scissors (Tokyo)

Hikari Scissors (株式会社ヒカリ), a Tokyo company established in 1967, states that it developed the convex blade for professional hair scissors and obtained Japan’s first patent for the blade-angle and polishing method. The company describes the profile as drawing on Japanese sword (日本刀) cross-sections, where the clam-shell form carries thickness behind the edge. No patent number, filing date or grant date is published on its current pages, so 1967 is the verified establishment year rather than a patent date.

Source: Hikari Scissors (Japanese)

Source trailSources and limits

The maker pages cited here describe their own convex constructions and publish no cross-brand radius, angle, grinding-stage count or price floor. Hikari’s origin and patent statements are first-party claims rather than independently verified records. No dataset located in this pass supports a market share, an adoption wave or a hair-health result for the section, so claims of that kind stay unsourced. Inner relief, edge finish and partner blade remain separate fields to verify on the exact model.

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