full inside 13mm/8inch

You should feel it hit the sphincter muscle, that stops the flow of urine, and stop & relax like you’re going to pee and that should let it go in further. Try doing it over a garbage can or the toilet. If that doesn’t work, try using a curved or flexible sound. The curve should be up 45 to 90 degrees. Once inside your body, the urethra goes up into your prostate & then your bladder. It’s possible your prostate is enlarged, common in me & many middle aged men, narrowing the passage, & preventing the sound from going all the way in. It does Not mean you are ill; you need to ejaculate more.