The 201 does take the Class 66 bobbins. It was built with the steel bobbins in mind, but my 201-2 will use any of the Class 66 bobbins, it don't care weather it's plastic or metal. Mater of fact all my machines that use the Class 66 will work with any of them.
That said, the only things I can think of that would cause a Class 66 bobbin to not fit this machine is:
>Your bobbin is not a Class 66; ( Class 66 bobbins have curved sides, while Class 15 bobbins have flat sides.)
>The bobbin is bent or somehow defective; a very definite possibility with some of the cheaper brands.
>There is something amiss in the bobbin carrier; lint, debris, thread, misalignment (?)
Sew-Classics does sell good bobbins.
Joe