INHDBOX 8mm 5/16" Fuel Non-Return One Way Check Valve Petrol Diesel Marine Aluminum Alloy Suitable:8mm (5/16") ID hose Overall Length:60mm Hex size:22MMHexagonal Length:21mm Compatible:Suitable for water, petrol, diesel, oils, and other fluids There might be a 1-10mm error on the basis of different measuring methods, it is in normal range. Pls measure the size before purchase.