Harry Lorayne's and Jerry Lucas' "The Memory Book"'s Peg System for remembering numbers.
You may notice slight discrepancies between the book's suggested pegs and the pegs in this set of flash cards. I found several (I believe) better alternatives to what Lorayne presented.
For example, 53 in "The Memory Book" is "loom". People no longer use looms, and I think it too unusual and hard to picture. So I replaced "loom" with "lamb". (Remember, it is about the phonetic sounds that count, not the consonants in the written word.)
The other ones I simply presented both the book, and an alternative that may be easier to picture.