Bifrustum

In geometry, an n-agonal bifrustum is a polyhedron composed of three parallel planes of n-agons, with the middle plane largest and usually the top and bottom congruent.

Family of bifrusta
Example: hexagonal bifrustum
Faces	2 n-gons 2n trapezoids
Edges	5n
Vertices	3n
Symmetry group	Dnh, [n,2], (*n22)
Surface area	${\displaystyle {\begin{aligned}&n(a+b){\sqrt {\left({\tfrac {a-b}{2}}\cot {\tfrac {\pi }{n}}\right)^{2}+h^{2}}}\\[2pt]&\ \ +\ n{\frac {b^{2}}{2\tan {\frac {\pi }{n}}}}\end{aligned}}}$
Volume	${\displaystyle n{\frac {a^{2}+b^{2}+ab}{6\tan {\frac {\pi }{n}}}}h}$
Dual polyhedron	Elongated bipyramids
Properties	convex

It can be constructed as two congruent frusta combined across a plane of symmetry, and also as a bipyramid with the two polar vertices truncated.

They are duals to the family of elongated bipyramids.