Symptom: When importing a SolidWorks file (.SLDPRT), it sometimes happens that TopSolid creates small planar surfaces in addition to the imported shape.

Cause : These surfaces correspond to user planes created in the SolidWorks file.

Solution: You can prevent these user planes from being imported by setting the TranslateWorkPlanes option to False in Tools > Options > Translators > Spatial translators > General.