Spi 12X18X3-A2 Granite Surface Plate Grade a 2-ledge

Product Description

The SPI 12X18X3-A2 is a Grade A black granite inspection surface plate used as a precision reference datum in dimensional measurement and quality control applications. Measuring 18 inches long by 12 inches wide by 3 inches thick and weighing 75 pounds, this plate provides a stable, flat reference surface for layout, inspection, and gauging work. The unit holds a unilateral flatness tolerance of 0.000050 inches, meeting the exacting requirements of precision metrology environments. Two accuracy certificates are included with each plate, and NIST traceability is provided. It is typically set up and used by machinists, quality technicians, and metrology professionals.

This surface plate is suited for use in machine shops, quality labs, and manufacturing inspection stations where a reliable flat reference is required. The 2-ledge configuration provides convenient support and positioning on a stand or bench surface. The black granite construction resists corrosion, does not burr, and maintains dimensional stability across normal shop temperature ranges. The included accuracy certificates support documented inspection processes and audit requirements.

Key Features

• Grade A flatness with 0.000050 inch unilateral tolerance
• Black granite construction for corrosion resistance and dimensional stability
• 2-ledge design for stand or bench mounting support
• NIST traceability certification included
• Compliant with ASME B89.3.7-2013, GGG-P-463c, ISO 17025, and ISO 9001
• Two accuracy certificates included with each unit

Compatibility

Designed as an OEM-style precision reference surface for use with standard surface plate stands and inspection bench setups sized for 12 inch by 18 inch granite plates.

Installation Notes

Surface plates should be installed and leveled by a qualified metrology technician or machinist. The plate should be positioned on a rigid, vibration-free stand or bench capable of supporting 75 pounds, with all three ledge points making consistent contact. Avoid dragging abrasive objects across the surface and protect the plate from thermal shock and impact. Periodic recertification of flatness is recommended to maintain measurement integrity.