The W&W #8, #9, D-9 & Singer 9W all have the same dimensions for the feet. Technically there are some minor differences in the way they fasten, The #8 machine however can use any of them with the "Exception" of any which use a driving arm, such as the ruffler. The drive arm on the #9, D-9 & 9W goes to the left of the needlebar, on the #8 it goes to the right so these will not interchange unless a drive adapter is made.
The shank of the #8 was designed so that the clamping screw had to be entirely removed to interchange, the others were all designed so the screw could be loosened & the foot changed from the side. On the #9 the foot was removed or installed from the right, on the D-9 & 9W to the left. By some manipulation however they will all interchange.
