24 to 30 ID X 0.250 (6.35mm) C/S Vulcanized Viton® (FKM/Fluorocarbon) O-Ring 75 Duro Black [VV75.250-030] : The O-Ring Store LLC, We make getting O-Rings easy!
Silicone O-Rings 6mm OD, 3mm Inner Diameter, 1.5mm Width, Seal Gasket Red 30pcs - Walmart.com
How do you measure an O Ring? – Rocket Seals
O-Ring Size Chart | USA AS568 Standard O-Ring Sizes