Cutex Brand Pack of 10 Singer Class 15 Aluminum Bobbins #2518A #2996A Pack of 10 Singer Class 15 Aluminum Bobbins Bobbin #2518A Bobbin diameter measures 20mm wide and 11mm thick Aluminum bobbins are considered the Top-End "Luxury Bobbins". They offer less resistance which translates to less drag to the bobbin thread tension For Singer models :15-30, 15-88, 15-90, 15-91, 31-15, 44, 233, 237, 239, 331K, 431D, 5102, 5107, 5122, 5123, 5124, 5127, 5522, 5528