stl file can't be mesh in Netgen

Hello
I create a .stl file include two solid parts. I use the same nodes of interface between two solids. But Netgen can't mesh the solid. It always shows inconsistent triangles. But if I seperately mesh the two parts, it works.

So how netgen mesh the composite solid? Or what's the format of .stl file?
I can't use .geo file because I think it can't create a complex geometry which defined by an equation.
I put my .stl file in attached.
Thank you!

Hi,
sorry the stl mesher is only able to mesh single solids. You could use the step or igs format and our opencascade interface.
Best
Christopher

Thank you. But when I use FreeCAD to transfer .stl file to STEP or IGS format, Netgen only draw the surface mesh not volume. I don't know why.

I put one of my STEP file in attached file.