Unless it's possible it came from somewhere else (someone put it there, it fell out of the sky, there was some other repair going on close-by), then I would turn the machine on it's back/side and see where there might be room (a big enough space) for a nut that size to fall out. If so, I would try to get to the spot from where it came, so I could put it back. You might have to take off part of the housing.
Look for a youtube video that discusses that machine or one similar - or a video that mentions a nut falling out of a Brother machine.
Have you tried sewing? Does it still sew OK?
A trip to the sewing machine repair man is going to be $150.00 or so. That might not be worth it.
Sorry I couldn't help more.
bk
Last edited by bkay; 04-03-2024 at 05:57 AM.