This was a response that Giangi posted in another thread. I poked around a bit for a chart, but didn't come up with one right away. Maybe someone else will post a link for you if I don't re-find it myself.
AGS GIRDLE GRADING:
Ext.Thin 0.00 to 0.08%
Very thin 0.09 to 0.50%
Thin 0.51 to 1.20% ---> AGS 0
Medium 1.21 to 1.70% ---> AGS 0
Sl.Thick 1.71 to 2.95% ---> AGS 0
Thick 2.96 to 4.20%
Very Thick 4.21 to 5.70%
Ext.Thick 5.71 % or more
No. It'll be more prone to chippiong if you abuse it. That is, keep hitting it against hard surfaces. Being thin in girdle size doesn't automatically mean it'll chip.