See the difference?

On the left is one of my oldest Kerr pint canning jars and on the right is one of my newest. The old one is very square and the glass is so thick my canning funnel doesn't fit down into it all the way. The new jar is thinner and rounded and doesn't interest me nearly as much!

By the way, I think the reason I have always preferred Kerr jars over Ball jars is because 1) my mom always used Kerr jars and 2) my name starts with a K and I loved to look at the pretty K on jars of fruit on the table when I was a child.