Brass Push Tube Fitting, Inch Tube OD Reducer

That's what it's built for. The larger end connects to 3/8 inch OD tube and the smaller end connects to 1/4 inch OD tube, so it handles that size reduction in one piece. No additional adapters needed in between. It's a push-to-connect style, so you're just pushing the tubing straight in until it seats. Brass construction holds up well in typical shop and industrial environments, and Numatics makes reliable fittings, so you shouldn't have any trouble getting a secure connection on both ends.

This fitting is constructed from brass, offering good durability and corrosion resistance for demanding environments where standard nylon might not hold up.