https://www.pipesandcigars.com/p/softy-pipe-bits-pipe-tools/1478264/
Can anyone who happens to have both sizes laying around give me internal diameter measurements in millimeters? What's the hole size for each of these? I'd really appreciate the bother. Or if you just have one size, maybe someone else can offer the other size.
I'm still interested in these Softy bit measurements, but as I waited, I dug. Found this video, and then by luck, I found some black vinyl tubing in that diameter. Used a little fine sandpaper to sand off the sharp edges because 1) when you cut vinyl tubing, the edge is sharp 2) because vinyl is harder, you can sand it vs not being able to sand rubber (if you needed to sand a rubber edge). The vinyl is surprisingly hard, but it is easy to work with if you let it sit in boiling-then-shut-off water for 10-15 seconds. I'm sure you could use a hair dryer with just as much success if you didn't want to mess with boiling water etc.
https://www.youtube.com/watch?v=qpEgSUbuAxI
provided by this user in this thread: https://www.brothersofbriar.com/t28653-one-of-my-fav-youtube-pipe-guys-and-softy-bit-alternative?highlight