I took these off my 1976 Bultaco Frontera in 1977 when I replaced them with air assisted caps. So I have had them hanging around my garage for a long time. With a digital caliper they show 28mm diameter, and 23mm tall. Two caps, the threads are good, O rings good, and I have one of the plastic push on cover. They install using the square of a 1/2" socket.