5mm outer diameter x 2mm inner diameter. Suitable for nitro glow fuel and petrol 2 stroke mixture. These have been heat treated however will melt if sitting on the exhaust. Its recommended to use heatproof tape or spring guards to protect the line. This fuel line is harder than silicone. These fuel lines have been precut to lengths of 1 meter so if ordering two 2 x 1 meter lengths will arrive.