Hey I have that same set of mixing bowls. They were a wedding gift, circa 1979. I'm sorry I broke the largest making bread in the first five years of its life. Been searching second hand stores ever since. :)
Imagine my surprise when she wrote and offered to give me hers?! Seems she'd found one in a thrift store and it was an extra at her house, would I like it? You can bet I answered that email the same day! I was amazed at her kind generosity.
Turns out it's similar in size to the medium bowl I have in this set, but hers has handles, now that's cool! I didn't even know those existed.
And the lid from the casserole set fits it, perfect for microwaving. I just love the 'Celebrate Fall' card she made to go along with it.