I posted this on another forum but got only 1 reply that didn't help at all. Maybe this group has the answer.

I want to get the factory fender flares for my 2009 Flareside F-150 and I see them from time to time, for sale on ebay. Most are take-offs from new trucks, but I am not sure if the two types of boxes take the same flares. They look to be the same openings and I know they both can be equipped with the flares. Does anyone know for sure if both boxes use the same flares?

Also, while we're on the subject....who knew that the flareside boxes were fiberglass on the outside?
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They been fiber glass for a while even on the ranger stepside

as for flares I would say get a set of aftermarket ones, the factory ones
attach with holes drilled in the side with push clip, not very easy to install. Were the aftermarket will mount with 3m tape and a few screws

 

Well...thanks for the info but I still don't have the answer to my question.

On to the next forum....

 

Flaresides have had Fiberglass fenders since 92.