Aeroquip SocketLESS 1/4 M Pipe

Carbon steel is standard for heavy-duty hydraulic fittings and handles the pressure demands of equipment like that without issue. The bigger factor in longevity is keeping connections clean during assembly and making sure the NPTF threads are properly seated. That tapered pipe thread design creates a mechanical seal on its own, which helps where you've got vibration or movement working against the joint over time.

For that hookup, it matches up as a -4 dash hose end on one side and a 1/4 inch NPTF male pipe thread on the other.