T-Lock Balance Shoes

What is the difference between the 15-195, 15-195B and the 15-229 shoes? I see they have "open cam" and "closed cam" in their part descriptions, but what does that mean? I'm going to measure my old shoes (that are broken in my window frames) tonight and want to order new cams for all the windows in our house........totaling 7 windows worth.

Thanks in advance,
David