Abstract: A brake drum gage is described for measuring the inside diameter of a brake drum of a vehicle with the wheel mounted on the vehicle in the presence of an axle tube and other undercarriage components or parts. The brake drum gage includes an elongate generally flat bar having proximate and remote ends and defines an elongate axis in a reference plane. A fixed element is fixedly mounted at the proximate end of the bar and a movable element is movably mounted on the bar for movements along the bar between the proximate and remote ends for adjusting the spacing between these elements. Each element includes a generally V-shaped arm that includes an upright portion generally parallel to the reference plane and an angled portion inclined in relation to an associated upright portion.