What are the different grades of gage blocks, and why do they come in sets?

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Roughness height rating micrometres, Ann (microinches, μǐnl AA 50 25 125 6.3 3.2 1.6 0.80 0.40 0.20 0.10 0.05 0.025 0.012 (2000) (1000) (500) (250) (125) (63) (32) 6 (8) 4 ) ) (0.5) Flame cutting Snagging Planing, shaping Drilling Chemical milling Elect. discharge mach Milling Reaming Electron beam Laser Boring, turning Barrel finishing Electrolytic grinding Roller burnishing Grinding Honing Electropolish Lapping Superfinishing Sand casting Hot rolling Forging Perm mold casting Investment casting Extruding Cold rolling, drawing Die casting The ranges shown above are typical of the processes listed. Higher or lower values may be obtained under special conditions. Key Average application Less frequent application Extracted from General Motors Drafting Standards, June 1973 revision FIGURE 10-49 Comparison of surface roughness produced by common production processes. (Courtesy of American Machinist.) FIGURE 10-50 Set of surface- roughness standards being used in a drafting room. (Courtesy of Surface Checking Gage Co.)