GM bolts are a unique combination of both metric and standard measurements. GM bolts can range from 6-14mm in diameter, with lengths ranging from 15-45mm. The threads on these bolts come in either standard or metric sizes, depending on the application they are used for. As an example, many GM vehicles use 12x1.5 thread size, which is a Metric measurement but designed to fit specific parts manufactured by General Motors (GM). While other manufacturers may produce components that require different sized fasteners, GM often uses its own proprietary designations for threaded fasteners. This allows them to ensure compatibility between their products and those made by other companies when servicing existing vehicles as well as creating new models with inter changeable parts.