1938–1940 Japan 10 Sen — Shōwa Aluminum Bronze Type
Shōwa 13–15 · Cu 95% / Al 5% · 22 mm · 4 g · holed type
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Each calendar year has an independent archive page. Mintage figures are retained as secondary Numista catalogue data unless an official annual quantity is separately verified.
Aluminum Bronze 10 Sen under the Temporary Currency Act
Japan Mint's museum guide identifies the 1938 10 Sen aluminum-bronze coin as a wartime issue created under the Temporary Currency Act, with a standard weight of 4.0 g, diameter of 22.0 mm, and composition of copper 95% / aluminum 5%. Japan Mint's special-exhibition list records the production period as 1938–1940 and measured 1939–1940 museum specimens at approximately 21.98 mm and 4.00–4.03 g.
Official Sources & Catalogue Cross-check
Japan Mint — Mint Museum Guide
Official Japan Mint museum material identifies the 1938 10 Sen aluminum-bronze issue and gives the standard as 4.0 g, 22.0 mm, copper 95% / aluminum 5% under the Temporary Currency Act.
Japan Mint — Mint Museum Special Exhibition Exhibit List
The official exhibit list records 1939 and 1940 10 Sen aluminum-bronze specimens at about 21.98 mm and 4.00–4.03 g, and states a production period of 1938–1940.
Japan Mint / Bank of Japan Currency Museum — Wartime Coinage Context
Official institutional material documents the wartime metal-policy changes that led Japan to replace or reduce strategic-metal coinage during the late 1930s and early 1940s.
Numista — Japan 10 Sen, Shōwa (N#14006)
Secondary cross-check for 1938–1940 dating, 4 g / 22 mm type data, 1.74 mm catalogue thickness, plain edge, holed form, inscriptions, catalogue identifiers and annual mintage figures. No Numista photograph, valuation table, logo or catalogue prose is reproduced.
Boundary note: 1940 also has a separate non-holed aluminum 10 Sen type in this archive. This folder covers only the 1938–1940 holed aluminum-bronze type.