Cosworth rings are a perfect match for your new Cosworth
pistons. Sold as a full engine set

P/N 20001515 Subaru WRX STI EJ25 (2.5L) 99.5mm
P/N 20001516 Subaru WRX STI EJ25 (2.5L) 99.75mm
P/N 20001517 Subaru WRX STI EJ25 (2.5L) 100.mm

P/N 20005160 Subaru WRX EJ20 (2.0L) 92.mm
P/N 20005161 Subaru WRX EJ20 (2.0L) 92.5mm
P/N 20003605 Subaru WRX EJ20 (2.0L) 92.mm(Use with Stroker pistons 20002489/ 20003685)
P/N 20003607 Subaru WRX EJ20 (2.0L) 92.5mm(Use with Stroker pistons 20002491/ 20003687)