High carbon steel you can check with a magnet once it is hot enough does not stick you can quench in oil to harden. Fitzo is telling you right on good files.
take 2 layers of masking tape and punch or drill hole in it same size as pin. Cover handle material with tape leaving pin material exposed. Finish pin to what you want. I've taken cratex wheels or rod in dremel and polished pin .
.250 is the standard but I have seen 3/16 in some also. 3/16 sounds good for what you want and I would chamfer the hole to not have any sharp edges to fray the cord.
I wish I could invite you all down here for the fun. 100 knifemakers plus 35 tables of supplies for us will be available. Saturday only with a scheduled dinner and get together afterwards at the Courtyard by Marriott Friday night to get to know each other. I am going to enjoy this!