[TenTec] TenTec model designation question

[FireBrick]

What is the difference ... if any between:
Ten-Tec 566 Orion II
and
just a Ten-Tec Orion II


??

I've seen ads for both ways but don't see the 566 designation in online 
descriptions.

Please and thank you.


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Don't be a sexist, broads hate that.
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Bill H. in Chicagoland
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