There are two basic types of hardness testing: Standard and Superficial. Each requires a slightly different instrument construction.

Ames standard testers read directly in these fifteen Rockwell scales:
   A, B, C, D, E, F, G, H, K, L, M, P, R, S, and V.

Superficial models are for testing case-hardened stocks, thin stock and soft materials in the Rockwell N and T scales.

Ames Hardness Tester model numbers tell you up to three things.

• The first number is the thickness in inches the instrument can test.
• The second number is the throat depth in inches, or how far in from the edge of the material tests can be made.
• The letter "S" at the end tells you this is for Superficial testing on the N and T scales only. ("ST" indicates a unique model for thin and tube stock.)