how to identify the difference of F2.115.2531 axial fan ?

here shows the two fans made from different factory.

one is made from ebmpapst Hungary, another is made from a oem factory.

1.material

look at this picture.

The left one is fake.Its material is rough iron.

The right one is genuine and its material is iron and plastic.

2.the back side of them.

look at this picture and check their difference of back side and their fans.

if you have them in hand, you can know their weight:

the fake is light, the genuine one heavy.

3.directions and arrows

Look at the picture.

The fake one have not directions and arrows.