Watch and learn about several of the different bobbin sizes, what machines they work in and how using the wrong size can affect your stitch quality.
Bobbin Work, National Sewing Circle
SEWING MACHINE BOBBINS, Plastic Bobbin, Metal Bobbin
CB-hook Bobbins and Bobbin Cases - Accessories - BERNINA
Understanding Different Bobbin Sizes, National Sewing Circle
What Bobbin Sizes Do I Need?
Sewing Basics: All About Bobbins - Underground Crafter
Long Bobbins, 5 Reproductions, for Singer and Many Other Vintage Sewing Machines, Read Description for Measurements and How to Wind a Bobbin
Understanding Different Bobbin Sizes, National Sewing Circle
Bobbin Work, National Sewing Circle
Bobbin Case for Singer 15-88, 15-90, 15-91, 15-125, 177C, 293B Sewing Machines Backward Latch 11 O'clock
Understanding Different Bobbin Sizes