Please keep in mind, that this is only one person's opinion, based on research and actual experience. As in all things relating to BDSM use your GOOD judgment. This outlines some of the things I have found out. Please know that I am not in any way a trained medical professional, I have not even taken a first aid class. I am not an expert, this information is just what I have found out.
Sounds are metal rods used in the medical community to dilate urethras, male and female.
Several styles are used in BDSM play. The store staff did not know what they were called. I found a surgical supply firm that was willing to copy several pages from medical catalogues. The type sold and Mr. S and LeatherMasters are called Hegar Uterine Dilators and are used on women. I started with a 5-6.