Hi, My name is Zeta and this is my first attempt to answer someone. I have a buttonholer some over 50 years and it still works fine on my singer that I bought in 1957.
The attachment fits on the sewing machine in place of the pressure foot. There is also an attachment that is screwed down over the
feet of the machine. The button sizer is put into the attachment
that controls the size of button hole you want.