Three Mother Letters
Seven Double Letters
and Twelve Simple Letters
These are the Twenty-two Letters
with which God engraved and made Three Sepharim,
and with them He created His Universe.
And with them He formed all that was ever formed,
and all that will ever be formed.
God Faithful King rules over them all from His Holy abode forever and ever.
One on Three
Three on Seven,
Seven on Twelve,
and all are bound together.
(Sefer Yetzirah)

 
In this picture can be seen all Twenty-two Hebrew letters.  The Three Mother Letters are in the triangle/pyramid; the Seven Double Letters are in the circle/sphere; and the Twelve Simple Letters are in the hexagon/cube.  The Three Mothers and the Seven Doubles are associated with the Ten Sefirot.  Their placement in this picture is according to that relationship:

Aleph א - Keter
Shin ש - Binah                                                         Mem מ - Chochmah
 
Gimel ג - Gevurah                Dalet ד - Tiferet                 Bet ב - Chesed
 
Tav ת - Malchut
(The Holy Palace precisely in the center)
 
Peh פ - Hod                          Resh ר - Yesod                     Kaf כ - Netzach

 
The Twelve Simple Letters start from the yellow Heh ה on the top part of the hexagon/cube, and proceed counter-clockwise.  These are associated with the twelve months of the year in Time; the twelve signs of the zodiac in Space (and the twelve edges of a cube as can be seen in this picture); and the twelve tribes of Israel in Soul.