A common question when it comes to measuring hoses and tubes is what to measure?  Do we measure the O.D (outside diameter) or the I.D (inside diameter or bore)? 

By 'hoses' we mean silicone or rubber hoses used for coolant, air, fuel, oil etc. By 'tubes' we mean tubes made from aluminium, mild steel, stainless steel etc to join the hoses together.

HOSES

Hoses are always measured by the I.D (inside diameter or bore). This is the important measurement. The outside diameter may sometimes be quoted in a technical drawing or such like, but this is not as important. Hoses are measured by the I.D because they fit over a metal/solid tube.

This hose above, as you can see, measures 32.10mm, so this is a 32mm inside diameter hose. All our hoses are listed with the inside diameter measurement.

TUBES

Tubes are always measured by the O.D (outside diameter). This is the important measurement. The inside diameter might be quoted on a technical drawing etc but this is not as crucial. Tubes are measured by the O.D because they fit inside a hose.

This tube above, as you can see, measures 32.18mm, so this is a 32mm outside diameter tube. All our tubes are listed with the outside diameter measurement.

Sometimes on hose joiners or aluminium tubes, like the one shown below, there will be a bead at the end to prevent the hose slipping off. This bead will of course measure a larger diameter than the main part of the tube itself. This is not important and does not need to be measured. When measuring a tube, always take the measurment of the predominent length of the tube - not the bead.