Accuracy Grade Classification of Granite Parallel Rulers (Granite Straightedges)
The domestic executive standard JB/T 7878-2017 “Rock Straightedges” divides them into three grades: Grade 00, Grade 0, and Grade 1, based on geometric tolerances such as straightness, working surface parallelism, and flatness. Grade 00 has the highest accuracy, and Grade 1 has the lowest.
I. Core Determination Indicators (Unit: μm, based on ruler length L)
The tolerance value increases with the length of the ruler body. The table below shows the straightness tolerance (main accuracy indicator) corresponding to common lengths; the parallelism tolerance is equal to the straightness tolerance:
Cuadro
Nominal Length L (mm) Grade 00 Grade 0 Grade 1
200 1.0 2.0 4.0
300 1.5 3.0 6.0
400 2.0 4.0 8.0
500 2.5 5.0 10.0
630 3.0 6.0 12.0
800 4.0 8.0 16.0
1000 5.0 10.0 20.0
1200 6.0 12.0 24.0
1600 8.0 16.0 32.0
2000 10.0 20.0 40.0
Supplement: The working surface flatness tolerance is 1.5 times the straightness tolerance of the corresponding grade.
II. Grade Application Differentiation
Grade 00 (Ultra-High Precision)
Metrology rooms, third-party testing agencies, CMM / precision instrument calibration, high-precision value transfer, used in constant temperature environments.
Grade 0 (Precision Grade)
Precision machine tool inspection, precision component inspection, mold industry, high-precision inspection stations in workshops.
Grade 1 (General Precision Grade)
General machine tool commissioning, general mechanical part inspection, equipment installation leveling, routine on-site inspection.
III. Supplementary Notes
Foreign products mostly refer to ISO standards. The grade labeling may differ slightly, but the tolerance logic basically corresponds to the domestic standard.
Accuracy testing must be conducted in a standard constant temperature environment of 20℃±2℃. Temperature deviations will directly affect the measured values.
For parallel rulers used in pairs, in addition to the accuracy of a single ruler, the set pairing parallelism will also be additionally sampled and inspected.
