I know this is a long shot, but I hate to waste vintage parts. My 403A is missing a tiny screw. It's one of the two on the bobbin case positioning bracket. I haven't got the machine sewing yet (instead I've been
taking it apart) but I assume it won't work well without this screw, right?
Here's a photo of the part:
Any ideas of where to find a replacement screw? And/or find out what size it is?