In a recent comment, Lorna asked if I used a template for the topstitching on my jeans fly. The answer is YES! Unfortunately, I can't seem to locate an internet source or even a reference for the notion(s) that I use so I don't know if it's still available. I don't remember where I bought it, but it's likely either Joann's or Nancy's Notions. I also don't know who makes it as there are no brand markings on the templates. Big lotta help I am, huh?
Still, I thought I would show you the template(s) and how I use them. If you ever see these for sale, I'd advise you to scoop them up. Also, if you're already familiar with these and know who makes them, please let me know. Edited to add: Thanks Belinda for a link to a source for these templates. You Rock!
This is the set of templates. With these two pieces, markings and measurements for 4 common fly widths are included, 3/4", 1", 1-1/4", and 1-1/2". There are also length markings on each end of the templates. I don't use those as my flys are always sized … er … on the fly. ;-) The circles are finger & thumb grips.
On the underside of each template are pointy "grabber" thingies. These hook into the center front seam gently, but strongly enough so that the template doesn't move.
This shows the template hooked onto the fold of the demo fabric. If this were an actual center front seam, the pointy grabbers would be hooked into the seam ditch. After the template is in place, I trace around the template with my chacoliner. The templates are made to be sewn around using a zipper foot, but I like tracing and just following my line. Less chance of cracking my template that way.
This is the chalk line tracing. I topstitch on this line using an open toe or a clear foot. If the fly is to have double topstitching as in the example at the top, I'll use a "toe" of the presser foot butted up next to that first stitching line for placement and my machine's needle positioning to adjust the spacing if necessary.
Since we're talking about fly topstitching templates, I thought I'd point out that zipper packaging includes a template. If you open the package carefully and then trim the bottom curve with scissors to finish the curve, you can use the back flap as a tracing template. These templates are 1-1/4" wide.
Oh, and here's a pic mentioned in a PR thread and nabbed from the Nieman Marcus website. These pants sold for $270. Is that $1 per pucker??