I have 3 vehicles and buy tires fairly regularly. -I've never heard of this term, even though I look into every aspect of size and performance, and everything printed on the actual tire. - I can only think it may be part of dealer ordering info or something like that.
OK, - I asked my tire dealer. -He says it's 'Master schedule part number'
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Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them