Granite Precision Square Accuracy Grade Classification Domestic Executive Standard: JB/T 10027-2017 “Granite Surface Plates, Straight Edges, and Squares”, classified by working surface flatness, squareness accuracy, and parallelism, divided into three grades: 000, 00, and 0. The smaller the grade number, the higher the accuracy.
I. Grade Positioning (Application Scenarios)
Grade 000 (Reference Grade)
Highest accuracy, limited to metrology rooms and constant-temperature laboratories, used for value transfer and standard gauge calibration.
Grade 00 (Precision Grade)
High-precision industrial use, used for CMM equipment commissioning, precision machine tool inspection, and high-end component quality inspection.
Grade 0 (Industrial Grade)
Regular workshop on-site use, ordinary machine tool installation, mold, and tooling perpendicularity inspection.
II. Core Tolerance Indicators (Unit: μm, using common specifications as examples)
Tolerances relax as the side length of the square increases. The following are the standard core limits:
- Squareness Accuracy (90° Perpendicularity, Core Indicator)
For the same specification: (\boldsymbol{Grade 000 < Grade 00 < Grade 0})
Small squares (e.g., 200×200mm):
Grade 000: ≤1.5 μm
Grade 00: ≤2.5 μm
Grade 0: ≤4.0 μm
Medium squares (e.g., 400×400mm):
Grade 000: ≤3.0 μm
Grade 00: ≤5.0 μm
Grade 0: ≤8.0 μm - Working Surface Flatness
Similarly follows the rule that the higher the grade, the smaller the tolerance, which is the basis for ensuring fitting measurement.
200×200mm:
Grade 000: ≤1.0 μm
Grade 00: ≤1.8 μm
Grade 0: ≤3.0 μm - Parallelism of Two Side Surfaces
Parallelism error of opposite sides, the limit rule is the same as above, used to control the overall geometric accuracy.
III. Supplementary Notes
Dimension Segments
The standard divides squares into multiple dimension segments based on the outer side length (200, 250, 300, 400, 500, 630mm, etc.). The larger the dimension, the larger the allowable tolerance.
International Benchmarking
Domestic Grade 000 ≈ International Grade AA, Grade 00 ≈ Grade A, Grade 0 ≈ Grade B.
Usage Differentiation
Grade 000 is mandatory for metrological traceability; Grade 00 is selected for precision machining / laboratory quality inspection; Grade 0 can be directly used for on-site production inspection.
