Here are a few shots of the Abrams side skirts. You can see from the underside shots of the right side #2-4 skirts that they are much thicker than #5 and #6 skirts. Those steel plates are still thick enough to stop small arms fire up to about a .50 caliber round.
From the top side of the skirts in the second picture, you can tell a ballistic armored skirt because it has a pair of bolts along the top edge (also much thicker). The bolts are removed and eyebolts inserted so the skirts can be handled by some type of material handling device such as a wrecker crane or M88 boom.
I've got two M1IPs, an early and a late M1A1. All four vehicles have the same side skirt set up.

