This Recommended Practice provides a common method to measure wear of friction materials (brake pad assemblies and brake shoes) and their mating parts (brake disc or brake drum). These wear measurements apply to brakes fitted on passenger cars and light trucks up to 4536 kg of Gross Vehicle Weight Rating under the Federal Motor Vehicle Safety Standard (FMVSS), or vehicles category M1 (passenger cars up to nine occupants, including the driver) under the European Community’s ECE Regulations. Measuring mass and thickness loss of friction materials (brake pad assemblies and brake-lined shoes) and their mating parts (brake discs or brake drums) is a common practice during most inertia dynamometer and vehicle tests. Mass and thickness loss are some of the main criteria to assess the performance and behavior of the wearable brake components. This makes repeatable and reproducible wear measurements a must. This Recommended Practice presents the default measurement methods for the parts in the friction couple. SAE J2986 can be considered as a companion document to supplement laboratory or vehicle test and measurement programs. The measurement methods presented in this Recommended Practice are useful to determine and report the mass and thickness properties (initial, intermediate, and final) of the friction couple or individual components. These measurements apply to brake parts preparation for mechanical testing, or other testing inducing wear or dimensional changes on the friction materials or their mating components.