Many GCS/SRS surgeons provide or recommend dilators manufactured by 
Soul Source 🔗 [Link: soul-source-sd.myshopify.com/collections/grs-vaginal-dilators/].  
My surgeon provided a set of custom made dilators (transparent lucite with a slightly different curve) but the diameters are standard #1-#4, and #5 exists.  I was told #3 is a goal because that is same width as a standard speculum used for annual exams.  
Each dilator contains marks to measure depth from 4-6 inches / 10-15 cm. 
I agree with jfong.  The surgeon will re-use what is possible and add a graft if necessary.  Final result for this method requires each patient dilates correctly after surgery.