This OEM Annovi Reverberi single piston fits various A.R. 18mm RC, RCA, and RCV series pumps. Measures approximately 30mm (length) by 18mm (outside diameter). The inside diameter width is approximately 8mm. If you have any other questions or are unsure if this piston will service your pump, please contact us through eBay. We are a full service pressure washer repair shop and an authorized Annovi Reverberi dealer.