Abstract: A set of gas turbine engine components comprises N gas turbine engine components. Each gas turbine engine component has a respective flow value. A method for selecting the N gas turbine engine components includes ordering the gas turbine engine components in dependence upon their respective flow value. For each ordered group of components a maximum range is determined for the respective flow values. If this maximum range is less than a pre-determined range limit then the ordered group becomes a set. If this criteria is not met then another component is added to the group, the group is reordered by flow value and the range check is repeated with allowable groups forming selected sets and further components being added as required.