\begin{table}%t5
%\centering
\par
\caption{Columns~1 and 2: projected virial radii 
of \mbox{A3921-A} and A3921-B; Cols.~3 and~4: virial mass estimates for A3921-A and 
\mbox{A3921-B}; Col.~5: mass ratio.
Masses are in $ 10^{14}~ {M}_{\odot}$ units and radiii in $h^{-1}$~Mpc~units.\label{Mass}}
\begin{tabular}{ccccc}  
\hline 
\hline 
$R_{\rm vir}$ (A) & $R_{\rm vir}$ (B) & $M_{\rm vir}$ (A) & 
$M_{\rm vir}$ (B) & $M_{\rm vir}$ (A) / $M_{\rm vir}$ (B) \\\hline
%
$0.39\pm0.02$ & $0.38\pm0.02$ & $\rm 4.3 ^{+1.4} _{-1.0} $ & 
$\rm 0.8 ^{+0.7} _{-0.3} $ & $\rm 5.2 ^{+4.4} _{-2.5}$ \\
\hline  
\end{tabular}  
\end{table}