How big are your balls?

After doing the trailer hitch for my bike I realized one thing I still needed was a nice shinny ball. Well I'm semi confused. I ended up just buying a 1 7/8 ball for the bike but is there really a reason for the different ball sizes? Not really talking about 3 inch but 1 7/8 and 2 inch is very close?







In the long run I figured $7 for a ball or two isn't as bad as the price of the attachment.