Those tracmasters are made by OTR wheel engineering in Georgia. They have a number of different tire sizes that will fit 12" wheels. 26x12, 25x12, 25x11, 25x10, 24x12, 23x10.50 and 23x8.50 and at least 4 different tread patterns
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http://otr.chattaninja.com/Lawn/Gard...-products.html
Im pretty sure the quote from Morrow tires was in regards to the 3 brand of ag tires they sell and didn't mean there were only three manufacturers.