Gearbox sprocket 21 Tooth, Norton AMC + laydowngearbox, 5/8" x 1/4". Suits Norton singles and twins with AMC gearbox from 1957. Can be used for Norton laydown gearbox with addition of the same spacer used on the AMC gearbox part 040131.Original Norton part number:040010 - axle sprocket (should fit E12/368 Norton laydown gearbox)