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SELECT DISTINCT patent.*, YEAR(date) as year FROM patent LEFT JOIN category ON category.patent = patent.patent AND category.type = patent.type WHERE (category.class = '313') AND (category.subclass = '231.21') ORDER BY date ASC, patent, type

Total of 1 patents found where: Class is '313'; Subclass is '231.21';

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T / S Patent Date Description Patentee Category Assigned To
 1935
U 2,011,136 August 13, 1935 Protective Apparatus
Arcing gap using flux control insulators		 AUSTIN, Arthur O.
 Arc Gap The Ohio Brass Co.

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