Learn from my mistake: NEVER use metal bobbins in a plastic drop-in bobbin case. Several years ago I had an old Kenmore front load machine and replaced it with a new Kenmore machine with a drop-in bobbin case. Because I had a lot of filled metal bobbins, I began to use them in the drop-in bobbin machine instead of using the plastic bobbins which came with the new machine. After several years of making quilts, the metal bobbins created grooves in the plastic bobbin case which eventually caused the machine to fail. The new bobbin case cost several hundred dollars to replace. I learned my lesson.