The 66951-004LF is a vertical card connector designed for single-row PCB mounting with 100-pin center spacing at 2.54 mm intervals. This connector features a 4-position configuration with mating pins specified as 0.025 inch (0.64 mm) square on true center, positioned within 0.015 inch (0.38 mm) diameter tolerance. The connector is rated for wave solder, infrared, or vapor phase solder processes with a peak temperature withstand of 260°C for 20 seconds, and includes 100% tin plating in the interface. The "LF" suffix indicates a lead-free option compliant with European Union directives. This connector is commonly used in industrial and commercial PCB applications requiring reliable vertical card-to-board interconnection with precise pin alignment and robust solder joint performance.