Sew the pant legs closed along the inseam, in the same manner as done previously with the side seam.
Repeat for the other side.
Either back your left fly (piece FF) with sateen, or apply a lightweight fusible interfacing to the underside.
Enclose the outer (rounded) edge of the left fly with the same bias tape you used on the center back seam allowances, and serge the centermost/straight edge.
Sew the left fly to the left front of the trousers along the centermost edges, right sides together, and leaving the bottom ⅝” of the fly hanging free.
Press the left fly over, toward center.
Understitch the left fly and seam allowances ⅛” from the seam line (again, leaving the bottom ⅝” of the fly hanging free).
Sew the two pant legs together along the center back and lower front – all the way from the upper back, to exactly where the left fly stitching ended – matching inseams and pinstripes. Reinforce the stitching beneath the left fly.
TIP: If you backed your pant legs with sateen, the pinstripes will probably not be visible on the underside. To aid you in aligning them across the seam, sew or baste through the relevant pinstripes in an easily-distinguishable thread color.
Press the seam allowances open.
Turn the left fly under and press.
Horizontally clip the right front seam allowance to the stitching where the left fly stitching ended.
Unzip your zipper.
Turn it over (right side down) and pin it into place along the right front, with the edges of the fabric and zipper tape flush.
Pull the left side of the trousers out of the way.
Using your zipper/piping foot, sew the zipper to the trousers, stitching close to the zipper teeth.
Then, using your all-purpose sewing foot, stitch again through both layers.
Zip the zipper closed and fold the upper left front back into place over the fly opening.
Pin the left front to the zipper.
Carefully “transfer” the pins to the underside, pinning the zipper to the left fly and unpinning the left fly from the front of the trousers.
Unfold the left fly from the front of the trousers.
From the wrong side, using your zipper/piping foot, sew the zipper to the left fly.
Switch back to your all-purpose foot and stitch the zipper to the left fly again.
Using your quilting/walking foot, topstitch the left fly into place through all layers.
(You can use the guideline on the printed pattern, but I prefer to simply stitch from the underside, using the edge of the left fly as a guide.)
You can back one of your right flies (piece EE) with sateen if you’d like, but it doesn’t make a big difference in the end result. (I did the fly, not the fly facing.)
On one of your right flies (piece EE), serge the outer/vertical edge.
On the other, bind the outer edge with the same bias tape you used on the left fly and center back seam allowances.
On the right fly piece you serged, trim away 1 ½” from the top.
Position this right fly piece underneath the right side of the zipper so the upper edges and seam lines are flush.
Note that the right fly will actually extend about ¼” past the zipper tape.
From the underside of the right zipper/fly, using your zipper/piping foot, sew the right fly to the trousers close to the previous (zipper) stitch line.
As with the left fly, leave the bottom ⅝” hanging free.
Trim the top of the zipper so the upper edges are flush, if you’d like – but if you trim past the zipper stop, remember not to zip your zipper up past where it should be! You don’t want to accidentally pull off the zipper pull tab!
