It looks like you're asking about a 3/16" x 1/4" compression adapter fitting. Here are some details about similar adapters:

• Material: Typically made of brass, which offers durability and corrosion resistance.
• Connections: One end connects to 3/16" tubing via compression, and the other end has a 1/4" male BSP (British Standard Pipe) thread.
• Applications: Commonly used for connecting copper, brass, aluminum, or plastic tubing in various systems, including water, gasoline, oil, vacuum, and air lines.
• Pressure and Temperature Ratings: These fittings usually have a pressure rating up to 400 psi and can withstand temperatures ranging from -65°F to 250°F