Standard Size, 15K Bobbins, These fit inside the 15k standard bobbin case present on most sewing machines from;

singer, pfaff, brother, Janome, new home.

Pack of 3 15k bobbins.

Fits Singer models 31-15 and 331, 1105, 1107, 1116, 1120, 1130, 1525, 3001, 3002, 3003, 3004, 3005, 3011, 3012, 3013, 3014, 4001, 4002, 4005, 4006, 4009, 4011, 4012, 4015, 4016, 4019, 4022, 5102, 5107, 5122, 5123, 5124, 5127, 5522, 5528. 

Fits all Singer machines that use Class 15 or 2518 metal bobbins.