The Gear Master was an accessory for the Sega Game Gear handheld game console. Manufactured by Beeshu, Inc., the Gear Master offered an alternative to the Master Gear peripheral, although both of these peripherals had similar compatibility issues. Just like the Master Gear, this accessory allowed Sega Master System games to be played on a Sega Game Gear. Unlike the Master Gear, the Gear Master cannot be screwed into the Game Gear unit.
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Gear Master Wikipedia(Text) CC BY-SA