sudas: I've looked up some more information. *Apparently, there is such a thing as cervical dilators. Their main medical use is for abortions. *Certainly, one should not mess with the cervix during a wanted pregnancy. *Those porn pros you mentioned may have used these dilators.
PS I'm not into injuring women or causing them real pain during sex.
Here is what member 35cm hanging /39.5cm attentio said in a post [edited for spelling] from Jan 2003,