This is a basic collar stay that I designed in three minutes based on a challenge on /r/functionalprint. It fits in two 80-character-column lines, or three for better legibility. The dimensions are probably wrong, since I never wear shirts fancy enough to put a collar stay into. That's why I haven't uploaded an STL. Open it in OpenSCAD and size it according to the shirt you want to use it in, or measure a collar stay that you already have. Just don't just print it out and then blame me that it doesn't fit.
It's three hulled cylinders, it doesn't get much more simple than that. Add $fn=50; at the top of the file if you want it to look smoother.
Print them on a 3d printer, or don't. I literally could not care less.
The collarstay_long file is not a longer collar stay, it's a longer file. By two lines.