Showing dimensions to fit a Shimpo RK2 wheel, its shaft is 0.983 in diameter. The molds fit down inside as shown, only contacting the cuphead at the shoulder.
2020 Project to Document a Shimpo Jiggering Attachment
Make your own jiggering attachment for your potter's wheel. Here are the plans and lots of help to get you going with molds and techniques.
Sign up at the home page.