Are 66 and L bobbins the same?
 

I think so, I'm trying to find out if I'm wrong.

I don't think so. L bobbins are for rotary hooks and are flat on top and bottom. 66 class bobbins aren't as wide, and are rounded on top and bottom.

The L Bobbin and the Class 66 Bobbin are different in the following ways;

Style L is flat and narrow with a width of 8.9mm and a diameter of 20.3mm where-as the Class 66 Bobbin is curved on the top & bottom with a width of 10.9mm and a diameter of 20.5mm

ps: The L Style Bobbin can be used in a Class 15 machine as the diameter is the same and the width is narrower so it fits and works fine. But you can not use the Class 15 Bobbin in a machine with the L Style Bobbin as the width (Class 15 Bobbin @ 11.7mm) is greater so does not fit. I have a few L Styles that i use with my 15-91 :thumbup:

The bobbins for the 66 are about rounded or raised over the top and bottom and just a wee bit smaller than the L bobbins. I recently had to buy more bobbins for my 66 and another Singer machine I have. They are available on Amazon.

The Singer 115 takes an L bobbin.