Triangular Bifrustum

C0 = 0.142857142857142857142857142857  = 1 / 7
C1 = 0.2474358296526967562182066202151 = sqrt(3) / 7
C2 = 0.285714285714285714285714285714  = 2 / 7
C3 = 0.989743318610787024872826480860  = 4 * sqrt(3) / 7
C4 = 1.73205080756887729352744634151   = sqrt(3)

V0 = ( C1,   C0,  C3)
V1 = ( C1,   C0, -C3)
V2 = (-C1,   C0,  C3)
V3 = (-C1,   C0, -C3)
V4 = (0.0,  -C2,  C3)
V5 = (0.0,  -C2, -C3)
V6 = ( C4,  1.0, 0.0)
V7 = (-C4,  1.0, 0.0)
V8 = (0.0, -2.0, 0.0)

Faces:
{ 6, 0, 4, 8 }
{ 6, 8, 5, 1 }
{ 6, 1, 3, 7 }
{ 6, 7, 2, 0 }
{ 7, 3, 5, 8 }
{ 7, 8, 4, 2 }
{ 0, 2, 4 }
{ 1, 5, 3 }
