| Granite Material | Use stable, fine-grained black granite with low porosity and consistent density. | Typical density: approximately 2.6–2.8 g/cm³; water absorption is commonly below 0.5% for suitable precision granite. | Request the material specification, density data, water-absorption test, and a sample surface inspection. |
| Square Geometry | The blade and base should be machined as an integrated precision reference tool, with a clearly defined squareness tolerance. | Common product specifications include 90° squareness tolerances from approximately 2–10 μm, depending on size and accuracy grade. | Ask for a dimensional drawing, tolerance grade, calibration method, and inspection certificate for the finished tool. |
| Flatness | The reference faces should be lapped or precision-ground and free from visible chips, distortion, and high spots. | Typical flatness tolerances range from about 2–10 μm for small and medium precision granite tools; larger tools may require a different tolerance. | Confirm the specified measuring area, tolerance zone, measurement equipment, and calibration status. |
| Surface Finish | Working faces should have a uniform, low-reflective precision finish without pits, cracks, resin marks, or uneven polishing. | A fine lapped finish is generally preferred for stable contact and repeatable measurement rather than a decorative polished finish. | Inspect samples under angled light and check contact behavior with a certified reference surface. |
| Available Sizes | Select dimensions according to the workpiece size, required reach, storage space, and handling capability. | Common blade heights are approximately 100–500 mm; custom sizes may be available for larger inspection applications. | Review a dimensioned drawing showing overall height, base length, thickness, working faces, and corner radii. |
| Dimensional Stability | The granite should be stress-relieved or properly aged before precision machining to reduce long-term movement. | Granite has low thermal expansion compared with many metals, but temperature changes can still affect measurement results. | Ask about quarry source, material aging, temperature conditioning, and recommended operating conditions. |
| Inspection and Calibration | Every production batch should be inspected against documented tolerances before shipment. | A complete report should normally include squareness, flatness, dimensions, visual condition, and inspection date. | Require a signed inspection report, calibration traceability, equipment details, and an agreed acceptance standard. |
| Quality Management | Prefer a documented quality system with controlled drawings, incoming inspection, process records, and corrective-action procedures. | ISO 9001 certification can support process control, but it does not by itself prove the accuracy of a specific ruler. | Check the certificate validity, certification scope, audit status, and actual production records. |
| Customization Capability | The supplier should be able to produce custom dimensions, tolerance grades, mounting holes, inserts, or identification marks when required. | Custom tooling commonly requires an approved drawing and may involve sample or setup charges. | Use a signed technical drawing with revision control, tolerances, material requirements, and acceptance criteria. |
| Packaging Protection | Use shock-absorbing protection, moisture control, corner protection, and a rigid export crate suitable for the tool’s weight. | Granite is hard but brittle; impacts can cause edge damage even when the main body appears undamaged. | Request packaging photographs, crate dimensions, gross weight, lifting instructions, and a drop-risk assessment. |
| Typical Production Lead Time | Lead time should include material preparation, machining, inspection, packing, and export documentation. | Standard items often require approximately 2–5 weeks; custom precision items may require 4–8 weeks or more. | Obtain a written schedule with sample approval, production completion, inspection, and shipment milestones. |
| Minimum Order Quantity | Choose a supplier willing to support the required order quantity without compromising inspection or packaging quality. | Precision granite tools are often quoted per piece; custom projects may have minimum quantities or setup fees. | Request separate pricing for one sample, a small batch, and the expected annual volume. |
| Commercial Terms | The quotation should clearly state product price, tooling, packaging, inspection, freight, taxes, payment terms, and delivery terms. | International quotations may use Incoterms such as EXW, FOB, CIF, or DAP; the included services differ significantly. | Compare quotations on the same specification and Incoterm rather than comparing unit price alone. |
| Supplier Communication | Technical questions should receive clear, consistent answers supported by drawings, photos, reports, and corrective-action records. | A reliable supplier should be able to explain tolerances, inspection methods, packaging risks, and nonconformance handling. | Use a written questionnaire and score response accuracy, response time, documentation quality, and engineering support. |
| Recommended Selection Weight | Prioritize accuracy and quality control over the lowest quoted price. | Suggested scoring: technical accuracy 30%, quality system 20%, inspection evidence 15%, material and finish 10%, delivery 10%, packaging 5%, commercial terms 10%. | Score at least three qualified suppliers using the same specification, sample process, and acceptance criteria. |
