This little hollow form is 3 1/4” in diameter and height with 1/8” thick walls. It was hollowed with my Trent Bosch stabilizer and Mike Jackofsky 1/2” hollowing tools. I’ve just ordered a set of the 1/4” Laurent Niclot mini hollowers from Trent, but couldn’t wait for them to arrive, so I had to go with a 1” opening. Hopefully once I’ve got the new tools, a much smaller opening will be possible.