With a 5mm hegar sound, I set out to see how deeply I could sound my uterus today! I pushed my tunnel plug into my pussy to put my cervix on display, then slid the sound into my cervix, navigating past the inner os and into my uterus. At the deepest point, I think I was hitting the far wall of my uterus! It's extremely sensitive there, but I just kept pushing the sound against it until I needed to cum.