Mike,
I was eying down OB's new Merry Widow design - 3/8x10 joint with an OB-1+ shaft which I know can be taken down to 11.75 because I have a few friends with OB shafts at that diameter. Though, it wasn't a plus shaft, it was an original I believe so maybe that makes a difference.
Was also looking at the Predator Classicos but I'm too big a fan of OB products to pass them up! =)
Are you sure that they have an OB-1 turned down, or are they playing with an OB-2? The hole in the front of an OB-1 is slightly larger than 1/4” diameter. If you turn it down to 11.75mm, you won’t have a lot of sidewall left on the shaft.