This listing is for 2 Pieces belt for many Singer vintage models. Belt part  # 193077.

If you have a Singer 66  series model , make sure it has a solid hand wheel (Not Spoked). 15-90, 66, 99, 206, 306, 319, 327, 328, 329 and many others. Belt  measures 15 3/4".

Here are a few more models belt will fit. 

Singer 127, 128, 15-88, 15-91, 185, 185k3, 206K, 223, 306k, 306w, 66-1,66-4, 66-6, 66-8, 66-14, 66-16, 66-18, 66-24, 99-13, 99-31  And many more.