Original style, Black  V belt  for many Singer vintage models . Very popular size for other makes and models also.  Belt part  # 193066  .

If you have a Singer 66  series model , make sure it has a Spoked hand wheel (Not Solid).  Belt  measures 13 3/4" circumference.

 New, Softer, better quality Black V-Belt . .   This is the best belt you can buy for your machine. Here are a few  models belt will fit.