I recently succumbed to my curiosity about urethral play and invested in a small collection of silicone sounds of various designs, diameters and lengths from siliconenozzles.com. Some of them can be seen in my gallery and I’ll add pictures of the others in due course.
Not knowing what to expect and heeding all advice to progress slowly and with caution I started off small at 6mm diameter (18 Fr) which proved to be a simple proposition and taught me that my curiosity was well founded as I found the sensations, experience and mind-rush to be fantastic. Having learned to understand the anatomy of my urethra from the sensations the sounds provide, particularly a 7.5” one named “Garter” whose ridges are pronounced, I’ve been able to fully insert my 7.5” sound the diameter of which ranges from 9mm to 13mm (39 Fr). That gives me sufficient “stretch” or intensity of sensation and I’ll likely not go much if any further.
As for length, 9” or thereabouts gets you inside the bladder which I have also done. Longer than that is pretty academic, although my long sounds are in the 11-15” range.
If this is something anyone is interested in experimenting with then be smart about it. Take it slow. Be hygienic. Listen to your body. Listen to @SwitchableSusie who, in various threads on his board, has offered her usual, candid and very sage advice.