Mine was 8mm, but I enlarged it and now it's 12mm.
All my life I wanted my slit to be bigger but I was too embarrassed to ask a doctor to do it. It seemed like it took forever to empty my bladder and the more vids and pics I saw of cocks with bigger slits, the more I wanted mine to be bigger.
When UP became popular in the early 90s I bought some sounds with the idea of stretching it over time. Although very enjoyable, the process was too tedious and looked like it might take forever. Finally, with all due care and in a sterile setting, I decided to clip it myself. The picture shows the before and after.
Three things resulted: 1) I like it much better visually, 2) my urine flow became much thicker and quicker, and 3) my cum shots were slightly less projectile in nature (whereas I used to splash the headboard when masturbating in bed, now I more often take it on the chin or the pillow if I don't aim up to take it mid-chest).
By the way, Zyz...you didn't list the length of yours. Like the penny pics, but would love to see a spread shot similar to mine or the other one in my profile album.
Would be interested to know if any of you have enlarged yours, and how you did it.
http://www.lpsg.com/members/stretchinit/albums/stretchinit%27s+gallery+pictures/660701-before-and-after.jpg