These are specific to SM play and it’s something called sounding where you shove a catheter in your urethra and it causes intense pleasure if done right. However I think this particular design is called a sounding rod? They can get really damn fat and I don’t know why someone would ever shove one bigger than their urethra entrance inside them.. a link if you’re curious about what they look like: https://www.amazon.com/OdontoMed2011-PIECES-URETHRAL-STAINLESS-DILATOR/dp/B073Y5Z2GZ/ref=asc_df_B073Y5Z2GZ/?tag=hyprod-20&linkCode=df0&hvadid=385644160795&hvpos=&hvnetw=g&hvrand=2611191096762077138&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9033260&hvtargid=pla-823676973318&psc=1&tag=&ref=&adgrpid=78925972976&hvpone=&hvptwo=&hvadid=385644160795&hvpos=&hvnetw=g&hvrand=2611191096762077138&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9033260&hvtargid=pla-823676973318

A catheter is used for surgical procedures and to treat diseases. Why are they used as a sexual act in yaoi/Bl?....I don't know and I wish they weren't