There are 10 heavenly stems and 12 earthly branches.

Each come with deep embedded meanings that are useful for both feng shui and bazi analysis.

Under the right conditions, stems and branches can combine or clash with other stems and branches when they meet.

Each heavenly stem has 3 interactions with 3 different stems consisting of one combination and two clashes.

Of the two clashes, one is an elemental clash while the other is a directional clash.

Heavenly Stems Combinations And Clashes

Stem Combination Clash
H1 H6 (Earth) H5, H7
H2 H7 (Metal) H6, H8
H3 H8 (Water) H7, H9
H4 H9 (Wood) H8, H10
H5 H10 (Fire) H9, H1
H6 H1 (Earth) H10, H2
H7 H2 (Metal) H1, H3
H8 H3 (Water) H2, H4
H9 H4 (Wood) H3, H5
H10 H5 (Fire) H4, H6

Legend here

Unlike the combinations and clashes of heavenly stems, combinations and clashes of earthly branches don’t have an observable pattern.

As such, the simplest way to present them is by defining the type of combination or clash.

Earthly Branches Combinations And Clashes

Seasonal Combinations
(三会)
E3+E4+E5 = Spring Wood
E6+E7+E8 = Summer Fire
E9+E10+E11 = Autumn Metal
E12+E1+E2 = Winter Water
 3 Combinations
(三合)
E12+E4+E8 = Wood
E3+E7+E11 = Fire
E6+E10+E2 = Metal
E9+E1+E5 = Water
3 Punishment Clashes
(三刑)
E3+E6+E9
E2+E8+E11
6 Clashes
(六冲)
E1+E7
E2+E8
E3+E9
E4+E10
E5+E11
E6+E12
Front Half Combinations
(前半合)
E12+E4 = Wood
E3+E7 = Fire
E6+E10 = Metal
E9+E1 = Water
Back Half Combinations
(后半合)
E4+E8 = Wood
E7+E11 = Fire
E10+E2 = Metal
E1+E5 = Water
6 Combinations
(六合)
E1+E2 = Earth
E3+E12 = Wood
E4+E11 = Fire
E5+E10 = Metal
E6+E9 – = Water
E7+E8 = Fire
Betrayal Clash
(相害)
E1+E8
E2+E7
E3+E6
E4+E5
E9+E12
E10+E11
Half Punishment Clashes
(半三刑)
E3+E6
E6+E9
E9+E3
E2+E11
E8+E2
E11+E8
Loss Clashes
(相破)
E1+E10
E3+E12
E2+E5
E4+E7
E6+E9
E8+E11
Self Clashes
(自刑)
E5+E5
E7+E7
E10+E10
E12+E12

Legend can be found here

Finally, don’t forget that elemental and directional clashes can also occur between stems and branches.

In view of this keep the fundamental concepts of the relationships between the 5 elements in mind.