Hard to say. It could be a spring loaded diaphragm that is designed to equalize pressure during fuel load changes since the system is returnless.
If you are cutting it to make it a return style rail, then get rid of it and use a standard regulator setup.
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black
