This is a KC-LINK 1812 series 5.1NF 500VDC ceramic capacitor with a C0G/NP0 dielectric material, specifically designed for high-frequency applications. It has a capacitance value of 5100 pF ±2% and operates at a maximum voltage rating of 500VDC. The capacitor is packaged in a 1812 (4.3mm x 3.2mm) metric case.