Before 1950’s, there were not companies specialized in the production of drumsticks. Manufacturers of drums and other percussion instruments used to produce and sell their own sticks. Also, there were not all the models we have in the market nowadays and also the sticks were named according to their application. Since that time, the three most common designations for drumsticks are “A”, “B” and “S”.
The letter “B” referred to “Band” and were made for use in theater bands, Big Bands and other orchestras.
The “S” referred to “Street” and these drumsticks were designed to be used primarily in marching and fanfare bands.
The reason for the designation of the letter “A” is a little vague. Apparently it identified drumsticks that did not fit in the category “B” or “S”. It is thought that perhaps the “A” comes from the phrase “All Purpose”. Other source says “A” is for “Acoustic”.
The numbers on the drumsticks are the reference to their size. In models “A” or “B”, larger the number, smaller is the stick. For example, a 2B is larger than a 5B and a 7A is smaller than a 5A.
Drumsticks for marching and fanfare bands are just the opposite; larger numbers are actually the larger sizes. For example, the 1S is smaller than a 2S, which is smaller than the 3S and so on.
These identifiers can be confusing and sometimes and it is difficult to find a reliable source to explain the exact system. Many of these details have been lost over time.
Source: Michel Stephan