The end that sticks into the hole is slightly flared, and that part measures 8.85mm in diameter. The non-flared part is 8.35mm in diameter. The widest part towards the front is about 10.3mm in diameter, and the whole jewel is about 11.42mm long. I have a number of other similar jewels available--just search my listings for "pilot light jewel" and they'll come up. Please see my pictures for details.
US shipping and handling is $5, and international is $18, no matter what quantity you buy. All my small parts are set up for combined shipping, so you can just use the "add to cart" feature and then check out at once to get discounted shipping. If you have any questions, please ask.
I have more pilot light jewels and other vintage electronics listed--feel free to take a look!