"These anodized billet 6061 aluminum adapter fittings allow an OEM fuel pressure regulator (FPR) or fuel pulse damper (FPD) to be reused in an application other than the OEM fuel rail. All fittings permit the unit to be clocked into the proper position." - Radium Engineering

Essentially allows OEM fuel system components to be affixed to aftermarket fuel rail kits, including the Radium Egineering fuel rail. 

Fitting Threads: 8AN ORB male
Fuel Pressure Sensor: 9.5mm Bore
FITS:
2023+ GR Corolla

Required: Fuel rail must have a 8AN ORB female threaded port.