SINGER 1725 - Manual (Page 56)

Sewing on buttons
Install the darning plate. (A)
Change presser foot to button sewing foot. (B) Select
zigzag stitch.
Position the work under the foot. Place the button on the
marked position, lower the foot. Adjust stitch width to "0"
and sew a few securing stitches. Set the stitch width to
number "3" - "5". Turn the handwheel to check that the
needle goes cleanly into the left and right holes of the
button (adjust the stitch width according to the button), and
slowly sew on the button with about 10 stitches. Adjust the
stitch width to "0" and sew a few securing stitches (1).
If a shank is required, place a darning needle on top of the
button and sew (2). For buttons with 4 holes, sew through
the front two holes first (1), push the work forward and then
sew through the back two holes as described (2).