Hi Paul
APC has made (at least) 3 versions of the 12x6EP prop:
* The original thin version liked to run around 8400 RPM, they quickly became a favorite.
* They brought out a thicker version with higher rated max RPM that needed something like 9600 RPM
* I got APC to revert somewhat and re-introduce a thinned out version as the 12x6 EP F2B. Part of the logic was that F2B flyers ran a relatively low RPM that was governed. APC did not go all the way back to the thin design but this version and likes to run around 8800 RPM.
I don’t know where the black prop fits. The lower price MIGHT mean it’s old (REALLY old) stock so it might be part of the original thin blade design. That would be a good thing because you can turn it slower and use less battery.
The “F2B” logo is in the mold, if it doesn’t show it then it’s likely not one of those!
My GUESS is that it is the thicker non-F2B design.
Confusing? No doubt!
Try comparing thicknesses along the props, or better still, just fly them back to back. Start with the F2B , check lap time then switch to the black prop. If it is the original design then it will likely fly faster than the F2B. If slower lap time then it is likely the thick version.