Model recognition points
1937 M20 500cc, sv, hand change, Brooklands silencer and fishtail. M21 600 cc, hand change, Brooklands silencer and fishtail.
1938 Generally as 1937, M21 had revised engine dimensions, otherwise unchanged.
1939 M20 and M21 with footchange and toolbox located  between chainstays on right. New oil tank, revised petroltank.
1940 M20 and M21 as 1939.
1945 M20 as in 1939, except no tank top instruments, toolbox altered, mudguards not valanced, rear carrier fitted.
1946 M21 as M20.
1947 No changes.
1948 M range: toolbox, battery carrier, petrol cap as on B group. During June 1948: the m models were fitted with telescopic front forks.
1949 Seald-beam headlights for all models.
1950 Unchanged.
1951 Plunger frame option, alloy head.
1952  Detail changes to brakes, dualseat option, new tank badges from March.
1953 New model numberplate, cowl and pilot lamp.
1954 Unchanged.
1955 Lock and cam as B range.
1956 M20 discontinued. M21 rigid and fitted with saddle as standard, plunger frame option.
1957 Unchanged.
1958 Unchanged.
1959 Unchanged.
1960 Unchanged.
1961 Unchanged.
1962 Unchanged.
1963 M21 discontinued.