I include here some pictures (and links to bigger pictures) of various outfits (or sets). Click on the pictures for a larger image. Outfits were numbered, with as many as eight basic sets available. The numbers were, in order from the smallest outfit to the largest: 00, 0, 1, 2, 3, 4, 5, and 6. Larger outfits were not sold in the US until the No. 7 of 1937; the No. 7 was introduced in England in 1924. "Linking" outfits were sold almost throughout the history of Meccano. These were called accessory outfits, and had an "A" after the number. If you had a No. 2 outfit, for example, you could buy a No. 2a outfit, combine it with your No. 2 and have the equivalent of a No. 3 outfit.
There were other accessory outfits at various times. The only ones sold in the US (at least that I am aware of) were the Inventor's Outfit (from 1916 - 1923; when the Inventor's B was introduced, this became the Inventor's A Outfit), the Inventor's B (from 1921 - 1923), and the Electrical Outfit (1921 - 1922).
For a listing of the outfits sold in the US from 1909 to around 1932, download the Meccano Price List (PDF). You will need the free Adobe Acrobat Reader to read this file.