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Baseball menko are an early type of Japanese baseball card, originally designed for use in the children's game of menko, but now avidly collected by baseball fans and card collectors. ("Menko" is both the singular and the plural form.)
The earliest known baseball menko, a generic baseball player, was from 1897.
The earliest baseball menko card set in Gary Engel's Japanese Baseball Card Checklist and Price Guide is from 1929, depicting black and white (or sepia) images of Big Six University players. They are called the "1929 Nichieido Seika B&W Photo Bookmark Menko."
Baseball menko exist in three shape categories: round, die-cut, and rectangular, and in a variety of sizes. The earliest die-cut and round menko sets cataloged by Engel are from 1947.
The "1947 Diecut Menko" are 1 3⁄8 inches (35 mm) wide by 2 3⁄4 inches (70 mm) high, with color caricatures of six NPB players, including star players Tetsuharu Kawakami and Hiroshi Ohshita (Oshita). The backs each contain: 1. A paper/stone/scissors symbol, 2. The player's family name in kanji, 3. The player's team nickname in katakana, 4. A line drawing of a generic baseball player, 5. A 5- or 6-digit number.
The "1947 Red or Blue Borders" round menko were 1 7⁄8 inches (48 mm) in diameter, with cartoon-like players on the front and blank backs. The team name in English, an arithmetic addition or subtraction, and the player name and sometimes position in kanji were also on the front.
Other baseball cards
There are a wide variety of Japanese baseball cards that are not called "menko", including bromides (blank-backed photos originally made with silver bromide paper); cards packaged with food, candy, and gum, including Calbee brand cards; game cards, including karuta cards and Takara brand cards; and the very numerous card sets issued since 1991 by Baseball Magazine SHA (BBM).
The book Sayonara Home Run!  by John Gall and Gary Engel contains a wealth of photos of a wide variety of baseball menko.
- Fitts, Robert K. (2001). An Introduction to Japanese Baseball Cards. RobsJapaneseCards.com, LLC, New York.
- Engel, Gary (2008). Japanese Baseball Card Checklist and Price Guide, 7th Edition. Prestige Collectibles, Santa Clarita, CA.
- Gall, John (2006). Sayonara Home Run!. Chronicle Books, San Francisco, CA.