These are inline Bosch competition fuel pumps, and it is generally recommend they be installed between the factory (or another aftermarket) in-tank fuel pump, and the fuel rail.  In addition, feeding these inline pumps with another pump (in series), will boost the output of the Bosch 044 fuel pump even higher.
    
   
Bosch 0580254044
   
Minimum current 12 Volts
   
Operating pressure 72.5 Psi (5 Bar)
   
Minimum flow @ outlet: 80 Gph (300 Lph)
   
High temperature reduction 8 Gph (30 Lph)
   
Inlet M18 x 1.5
   
Outlet M12 x 1.5
   
Positive M6 / negative M5 electrical connections