My Singer bobbins are slightly bubbled compared to the Elna which are flat. The Elna will deal with the Singer bobbins but the Singer will only work with Singer bobbins and only the bubbled type that it came with. My old Euro Pro mechanical and my Voyager quilting machine take the same metal bobbins & use the same pin on the bobbin winder. The plastic ones use a different pin and the bubble-type Singer bobbins are more apt to wind incorrectly because the bubble butt makes them wobble.