Why do some SMA connectors have a rectangular center pins?
Looking at some of my own radio equipment, I found that one SMA connector has a square pin like yours. I never even noticed the different pin, and there is no noticeable difference in its performance.
I would assume it's for a stronger solder joint, as solder bonds to flat surfaces better than it does to curved surfaces, but I could be wrong, so don't quote me on it.