\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}
\usepackage{tikz}
\usepackage{tikz-3dplot}
\usetikzlibrary{shapes, calc} 
\begin{document}
\begin{preview}
\tdplotsetmaincoords{70}{0}
\begin{tikzpicture}[tdplot_main_coords]
    \def\RI{2}
    \def\RII{1.25}

    \draw[thick] (\RI,0)
      \foreach \x in {0,300,240,180} { --  (\x:\RI) node at (\x:\RI) (R1-\x) {} };
    \draw[dashed,thick] (R1-0.center)
      \foreach \x in {60,120,180} { --  (\x:\RI) node at (\x:\RI) (R1-\x) {} };
    \path[fill=gray!30] (\RI,0)
      \foreach \x in {0,60,120,180,240,300} { --  (\x:\RI)};

    \begin{scope}[yshift=2cm]
    \draw[thick,fill=gray!30,opacity=0.2] (\RII,0)
      \foreach \x in {0,60,120,180,240,300,360}
        { --  (\x:\RII) node at (\x:\RII) (R2-\x) {}};
    \end{scope}

    \foreach \x in {0,180,240,300} { \draw (R1-\x.center)--(R2-\x.center); };
    \foreach \x in {60,120} { \draw[dashed] (R1-\x.center)--(R2-\x.center); };
\end{tikzpicture}
\end{preview}
\end{document}
