The VRT3-310EZ Unloader with 4,500 max PSI, 10.5 max GPM and 3/8"F outlet, black spring and adjustment knob. 
 
Includes built-in HD EZ start valve for no-load start up that minimizes back pressure until unit is powered up. The unloader valve diverts water flow into bypass when the trigger gun valve is closed. Unloaders may be designed to respond to either an increase in pressure or a change in flow. The unloader valve may also be used for variable pressure adjustment. This is one of the most versatile and reliable unloaders available.
If NO Easy Start feature is required, use alternate unloader without EZ Start valve: VRT3-310A
 
SPECIFICATIONS
Max GPM10.5Max PSI4500Inlet2x3/8" FOutlet3/8" FMax Temp194° FBy-Pass2x3/8" FSpring ColorBlackKnobYes