Vintage and Veteran, 1907 – 1929

In the early years of motorcycle production, the Douglas factory simply used sequential numbers for frames, engines and gearboxes. These numbers related only to the individual assemblies and did not match. By the early 1920s however, with production rising steadily and the sequences for engines and frames approaching 99,999, prefix letters were added and number sequences restarted.

Frame Number Location

  • Pre-1925 – Rear frame lug above gearbox, nearside or offside
  • Post-1925 – Junction of saddle/tank tubes, nearside
  • OHV Models – Gearbox mounting, nearside

Engine Number Location

  • Beside base of rear cylinder or nearside magneto platform

Gearbox Number Location

  • Top of gearbox, or on small nearside mounting lug

Example 1 1915 2.3/4 HP – Frame 24185, engine 24627, gearbox 23913
Example 2 1924 Model OB 600 OHV – Frame HF 391, engine OE 273, gearbox PG 407

Post Vintage, 1930 – 1939

With an expanding model range, the ability to distinguish between different frames, engines and gearboxes became more critical. Each model now had its own specific frame and engine number, although these remained non-matching. Gearbox types generally related to machine size – lightweight or heavyweight – and performance, and gearboxes with the same number prefix could be found in different models, eg: RG/H **** could be fitted to a 1932 350 Terrier, a 1932 500 Bulldog or a 1934 250 Comet – all ‘lightweight’ machines.

Frame Number Location

  • Usually at the junction of the saddle/tank tubes, nearside or offside

Engine Number Location

  • On top of crankcase beside magneto, front or rear

Gearbox Number Location

  • Top of gearbox, offside

Example 1936 Aero 500 – Frame AE 263, engine 5/L 173, gearbox M 386

Post-War, Mark Series 1947 – 1954

Post-war, with the advent of the new T35 ‘Mark Series’ models, Douglas changed the numbering system again. Now, engines and frames were stamped with matching numbers. Gearboxes were stamped with a separate, sequential number, although some gearboxes were unstamped.

Frame Number Location

  • Headstock, nearside

Engine Number Location

  • Usually by nearside cylinder base. On early machines, may be behind offside cylinder

Gearbox Number Location

  • Top of gearbox, offside

Example 1951 Mk. V – Frame 10587/5B, engine 10587/5, gearbox 7697

Dragonfly, 1954 – 1957

For the final years of production, Douglas adopted matching frame, engine and gearbox numbers for the Mk. VI, better known as the Dragonfly. All three assemblies had the /6 suffix.

Frame Number Location

  • On plate above swinging arm mounting, nearside

Engine Number Location

  • Cylinder base, nearside

Gearbox Number Location

  • Top of gearbox, offside

Example 1956 Dragonfly – Frame 1240/6, engine 1240/6, gearbox 1240/6