Use the documented measurement point.
The manufacturer’s measuring guide refers to inside diameter at the air-intake opening. A vehicle may have more than one connection point, so use the relevant vehicle and component documentation before taking a measurement. Do not infer a model from the outside of a hose or a photograph.
Record the unit.
Write down whether your measurement is in inches or millimeters. The catalog chart publishes inch dimensions for the Standard Ki series. Keep fractional measurements intact: 2 3/8 inches is 2.375 inches. The workshop finder uses those published values rather than guessing the closest size.
Check the model group.
Standard intake, Carburetor and European are separate catalog groups. A number in a code is not enough to establish the dimensions of a different group. For codes without a published diameter, email the full code and your measurement.
Match the reference, then order.
Use the full model chart to compare codes and dimensions. Email the brand name, code and quantity you want. Include the measured opening and any relevant vehicle details so the order discussion is about the correct part.
Manufacturer’s measuring guide · Tornado size finder · Cyclone size finder