Abstract: A brake drum gauge comprises a U-shaped frame with a pair of supports attached to its ends so the gauge may rest on the rim of a brake drum. A micrometer having an outwardly biased actuating pin is attached to one end of the frame, and a reference pin is attached to the other end thereof. The reference pin and micrometer actuating pin engage the inner surface of the brake drum at diametrically opposite points, the micrometer thereby indicating the diameter of the drum relative to its prescribed nominal diameter. The reference pin and support attached to the same end of the frame may be elements of a set of interchangeable pins and corresponding supports, whereby the gauge may be selectively fitted to measure brake drums of different sizes.