FSCurveFillet describes a curve Shape feature of Curve Fillet type which instance could be created selecting the button.
Standard > Feature > Visualizable > SkmDrwPackage > 2DGeometry > SkmDrwPackage > 2DCurve > FSCurveFillet
FSNet describes a surfacic Shape feature of FreeStyle Net type which instance could be created selecting the button.
Standard > Feature > Standard > Visualizable > MechanicalModeler > GeometricFeature > MechanicalModelerHide > Body > BasicWireframePackage > Wireframe > BasicWireframePackage > Surface > FSNet
FSSweep describes a surfacic Shape feature of FreeStyle Sweep type which instance could be created selecting the button.
Standard > Feature > Standard > Visualizable > MechanicalModeler > GeometricFeature > MechanicalModelerHide > Body > BasicWireframePackage > Wireframe > BasicWireframePackage > Surface > FSSweep