The widest transverse diameter of the fetal skull is
Transverse diameters of fetal skull are

Biparietal diameter: 9.5cm
Super-subparietal: 8.5cm
Bitemporal: 8cm
Bimastoid: 7.5cm
Biparietal diameter
Occipito-frontal diameter
Bitemporal diameter
Suboccipito-frontal diameter