1997 Chevy Tahoe what tools required to make repairs

Brakes problem
1997 Chevy Tahoe V8 Four Wheel Drive Automatic

I'm going to do my own brakes and rotors, but i need to know what size that allen hex bit socket is suppose to be. i bought a 3/8" but it seems to big is this a metric size required? can you tell me the proper size the calliper is suppose to be please?...