Keep in mind ANZI Z87 rating is different for goggles, glasses, and face shields.
ANSI Z87.1-2003 rating means that goggles will survive a 1.04gram 6.35mm steel bb shot at it at 250fps from 50 inches away at 20 different impact points, or approx. 3J or 570fps w/ .20g.
Glasses (vs goggles) that are z87.1-2003 rated only have to survive a 150fps shot for the same rating.
That is only 1.08J, or roughly 345fps with a .20g bb.
Just a warning...