Step 1: Create a Template
Cut out the paper template, trace around it on more paper and cut out the second template. One is your front, the other is your back.
For each side, wrap the paper in place around your fob. Feel around carefully to understand where your buttons are. I used my fingernail to score the paper, then I went over those marks with a pen. Cut out the paper template and fold it in half lengthwise to see if it is symmetrical. Adjust as needed, paper is cheap.
Optional step: Before cutting my only scrap of leather I used the template on some duct tape folded sticky sides together. This was my "practice leather." It helped me refine the shape of the template and see if the button placement was good with a thicker material than paper.
Transfer your templates to the leather's wrong side and cut them out.
Step 2: Close Those Windows!
Note: Be careful not to get your fingerprints on the sticky side of the packing tape. The idea is to create a clear window and your fingerprints will ruin that.
First cut out a small piece of clear packing tape and carefully place it sticky side UP over a button opening. Then cut a much larger piece and put it sticky side down, creating a window that has lot of grip on the leather on all sides.
Step 3: Attach the Grommets
You will attach two grommets, one for each piece for leather. (When you insert your key ring though the final fob holder the ring acts as a lock so fob can't fall out.)
Step 4: Sew It Together
You can use whatever sewing technique you like. I wanted a tight seam so I used two needles and sewed the pieces together like I was lacing up some tennis shoes. I left the stitches loose until I was done so that I could "tighten the laces" on the fob for a custom fit. Think of this as a tiny little key fob corset. Perhaps this technique has a name, I don't know it.
Step 5: Put It to Work!
How well does this hold up? The photos from the first part of this instructable are from when I first made this two years ago. The photos from this page are from today just after I replaced the packing tape window, which had become a bit worn looking. I expect the leather holder will last for more years to come. I hope this helps someone out. If you build this, please leave a comment.