I bought two 10 packages of Dritz brand Class 15 metal bobbins at JoAnn fabrics. Out of the 20 bobbins more than a fourth were so crooked they wobbled on the shafts and caused trouble in the bobbin case.
Of the Class 15 bobbins I've bought from Sew-Classic All of them are good and useable. Same with the Class 66 and other bobbins too.
Joe