Inline manual shut off valve - 1/4" (6mm) Pipe to 3/8" (10mm) Pipe

3/8" pipe to 1/4" pipe Inline Manual Valve

This fitting is typically used to connect a section of 3/8" (10mm) piping to 1/4"piping together. It then also allows you to open or "shut off" the flow of water through the pipes to an endpoint.