Yep that's for spinning the other direction. I have a Derale 6-blade, used it for about two weeks (until I came across an OE 7-blade that I'm still using).
The Derale is 18" diameter, a little heavier than the viscous units but it's yours if you want it..I also have a 20" (19-3/4" actual) 5-blade viscous fan that was off an RV if I remember...it's used but other than being a little dirty it's fine. It was a tad too big for my shroud. You can have either one, free, just p.m. me a shipping address if you're interested..
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