This license plate mount is a direct bolt on for open belt drive primary on Harley-Davidson motorcycles with a 4 speed transmission

a wheel spacer

and it's got some real heft to it

used on 1921-1923 JD and 1924-29 J

#8304 PARK Complete Stock Hardware Kit - 1937-1939 Harley-Davidson 74 & 80 Cast Iron Head - Parkerized Inside Diameter_.813" This license plate mount isComplete stock hardware kit for Harley Davidson 74 & 80 Side Valve with cast iron heads 1937 1939, parkerized. Each kit contains all the stock motor nuts, bolts, washers and studs for your motor. The kit includes primary cover screws, lifter base screws, circuit breaker screws, case studs and nuts, timing plug, cam cover screws, cylinder base nuts and washers, oil pump nuts and bolts, transmission side cover nuts and washers, transmission top screws,