Guess what? A thumb screw, is called a thumb screw because you're supposed to tighten it with your fingers (and thumb).
My finger strength isn't the best, and I find the little sewing machine screwdrivers really hard to use, SOOO, I've been using a regular screwdriver to tighten the screw that holds the pressor foot in place.
Today, I snapped it off. Luckily I was able to get the threaded part out of the post.
When I went to the dealer, she told me NEVER to use a screw driver to tighten that screw. Sorry, that's not going to happen. When I finger tighten it, it loosens and I've broken needles that way. (Um, then why is there a slot for a screwdriver????)
But, I will be more careful
It was a less that $10 fix, thankfully.
I still don't like wobbly feet though.