Square block (as per GB7-62) is an important auxiliary tool in the plate measurement. It is used for inspecting and measuring the tridimensional lineation by fitters, the parallelism and verticality of machining parts, as well as various location differences.
| Type (mm) | Parallelism of working surface | Flatness of working surface | Perpendicularity of working surface | |||
| Precision grade (μm) | ||||||
| 1 | 2 | 1 | 2 | 1 | 2 | |
| 100 × 100 × 100 | 2 | 4 | 2 | 4 | 2 | 4 |
| 150 × 150 × 150 | 3 | 6 | 3 | 6 | 3 | 6 |
| 200 × 200 × 200 | 4 | 8 | 2.5 | 4 | 4 | 8 |
| 300 × 300 × 300 | 6 | 12 | 2.5 | 4 | 6 | 12 |
| 400 × 400 × 400 | 8 | 16 | 4 | 8 | 8 | 16 |
| 500 × 500 × 500 | 20 | 40 | 5 | 12 | 20 | 40 |
