Not only does size matter, so does material! Don't use metal bobbins in a machine that is designed to use Plastic bobbins! Found that out the hard way, my "new" Kenmore (Janome style) machine will "take" the metal Singer bobbins I've owned forever, but it just doesn't quite feed right! Lot's of jams and snarls! (machine and human!) So I only use those old "mini-spools" for the top thread, if I need that specific color. I'm fairly safe, those bobbins haven't seen the daylight for years! and it's only for very small projects!
When I purchased a Husqavarna-Viking Sapphire 835, I purchased a "bag" of 20 bobbins, and am now looking to purchase more. It's so handy to do large projects with a set of "pre-filled" bobbins! But no way would the Kenmore plastic or Singer metal bobbins EVER get near the HV!
NEVER feel silly asking any questions, we have all had them and this Quilting Board is the BEST place I've found to post and get helpful answers!