Some calipers have inspection holes in the caliper body. If they do not, the brake pads can be visually inspected from the outer ends of the caliper.
On a floating caliper, examine the mounting pins for rust that could limit travel. Most manufacturers recommend that these pins and their bushings be replaced each time the caliper is removed.
On a fixed caliper, check the pistons for sticking and rebuild the caliper if this problem is found.
Some sliding calipers use a support key to locate and support the caliper in the anchor plate.
A sliding caliper with suport plates (keys).
The caliper support key is inserted between the caliper and the anchor plate. A worn support key may cause tapered brake pad wear. Always inspect the support keys when replacing brake pads.