These O-rings fit on the lower spacer that makes up the difference between the Injector dynamics injectors and the housing for the injectors. This is a crucial area for fuel leaks so you want to make sure you have a good seal here. Fits  on most Subaru cars.

Set of four O-rings.

Fits all 2002-2014 Subaru WRX, and 2007-2021 WRX STI. Does NOT fit BRZ/FR-S/Toyota 86.