I would either take a caliper with me to someplace that sells them, or go to the library, and in the crafting section, look for a book on home crafts and check there. You might be able to find it online too... But i would guess it's about 30mm-50mm in diameter...
ohhh thrift store is a great place to find odds and ends to use for measurements for modeling. Lots of great finds there
I forgot I have one at home! Now I have to remember to bring it back with me after lunch.I learned a long time ago the wisest thing I can do is be on my own side, be an advocate for myself and others like me. -Maya Angelou
email@example.com Community Advocate