Classification of Accuracy Grades for Granite (Rock) Measuring Tools, based primarily on National Standard GB/T 20428-2006 “Rock Slabs” (mainstream grades are Grade 000, 00, 0, and 1; the old standard GB 4987-85 is the same). The core indicator is flatness, with tolerances calculated based on dimensions and diagonal length.
I. Grades and Core Definitions (National Standard)
Grade 000 (Calibration Grade / Metrological Reference)
Highest precision, used in National Metrology Institutes, calibration laboratories, optical/semiconductor references
Flatness Formula: 1 × (1 d/1000) μm (d = diagonal mm)
Example: 300×300mm → ≤1.5μm; 1000×1000mm → ≤2.5μm
Grade 00 (Precision Inspection Grade)
CMMs, vision systems, precision inspection references
Formula: 2 × (1 d/1000) μm
Example: 300×300 → ≤3μm; 1000×1000 → ≤5μm
Grade 0 (General Inspection Grade)
Workshop precision inspection, tooling and fixture references
Formula: 4 × (1 d/1000) μm
Example: 1000×1000 → ≤7μm
Grade 1 (Ordinary Scribing / Rough Inspection)
Mechanical scribing, general assembly inspection
Formula: 8 × (1 d/1000) μm
Example: 1000×1000 → ≤14μm
II. Quick Reference Table for Common Specifications (μm, 20℃)
الجدول
Specification (mm) Grade 000 Grade 00 Grade 0 Grade 1
300×300 1.5 3 6 12
500×500 2 4 8 16
1000×1000 2.5 5 10 20
1500×1000 3 6 12 24
2000×1500 4 8 16 32
III. Other Key Precision Indicators
Surface Roughness: Working surface Ra≤0.02~0.1μm (Grade 000/00)
Straightness (Straight Edge): Grade 00 ≤1μm/m, Grade 0 ≤2μm/m
Perpendicularity (Right Angle): Grade 00 ≤2μm/100mm
Parallelism (Parallel Rule): 1/2~1/3 of the flatness of the same grade
IV. Grade Selection Guide
Grade 000: Metrological calibration, semiconductor mask inspection, optical references
Grade 00: CMMs, precision inspection, aerospace
Grade 0: Workshop quality inspection, tooling references, precision assembly
Grade 1: Scribing, rough inspection, general assembly
V. Comparison with Metal Platforms
Granite: Grade 000/00 stable, resistant to temperature changes, wear-resistant, rust-proof
Cast Iron / Steel: Highest Grade 0~1, easily affected by temperature, vibration, and rust
