GM Motors uses SAE (Society of Automotive Engineers) standards when it comes to their production and engineering processes. This means that all parts they produce are designed according to the specific measurements and tolerances as outlined by the SAE. For example, a typical automotive engine will have an inner diameter defined in terms of inches or fractions thereof, along with other critical measurements such as thread sizes, bolt lengths etc., all specified in imperial units. Metric units may be used for some components but generally this is kept to a minimum given that most customers would prefer standardised parts which fit with existing vehicles on the road today. As GM Motors has been around since 1908, many of its original designs were based on SAE standards so these remain largely unchanged even though metric systems have become increasingly popular over time.