I was working on a door in my 1935 house and noticed that each hinge pin has a C rings about 1/4 inch down from the top.  The ring is relatively wide compared to it’s diameter, like the rings which go around a piston in an engine.  I assume this helps keep the pins from working out. 

I’ve never noticed this before and I’ve removed a fair number of hinge pins.  Everything else about the hinges on this door is perfectly ordinary.  The hinges are stamped Stanley.

My questions are: 

1)  Is this unusual or have I just failed to observe it before?

2)  If I wanted to buy a similar hinge pin, how would I specify it?