Ibhola yangaphandle engqukuva yebhola eneneni iyantlukwano yebhola yegroove enzulu, ebonakaliswa ngumphezulu ongqukuva wedayamitha engaphandle yeringi yangaphandle, kwaye inokudityaniswa kwi-concave sphere ehambelana nesitulo sokuthwala ukudlala indima ukulungelelanisa. Ukuthwala kwe-spherical yangaphandle kusetyenziselwa ikakhulu ukuthwala i-radial kunye ne-axial edibeneyo yomthwalo esekelwe kumthwalo we-radial, kwaye ngokuqhelekileyo ayifanelekanga ukuthwala umthwalo we-axial wedwa.