There are a lot of "folding knife" style key holders, key bars or key bones. Most, if not all of them, require screws with the correct length. Screws that needs to be re-tightened now and then, to give the right friction or just to keep it from falling apart.
This key holder integrates a standard 4 mm nylon cable tie instead, so you can keep any number of keys in it. Just print and zip it up!
You'll need at least one nylon cable tie (zip tie), 4 mm wide. One with length 250 mm or two shorter ties. Print pieces A+B+C if you have a long zip tie, or pieces A+A+C if you have two shorter ties.
Edit: There is now also an optional part D available. It is a 1 mm or 2 mm shim, use one or more to stabilize your key holder or just make it more colorful.
This is an easy print without supports, and it should print in about an hour at 0,200 mm Z. I used PLA, and printed with fans on full speed so it bridges well when covering the hollow parts.
You will figure it out how to assemble this thing looking at the images. There is also an optional shim, and an extension (put it under the zip tie lock) included so you can connect any car key or fob.