 Terumah  

 26:19 
Place 40 silver bases under the 20 beams. There shall be two bases under each beam, one [to hold] each peg.
Ve'arba'im adneychesef ta'aseh tachat esrim hakaresh shney adanim tachathakeresh ha'echad lishtey yedotav ushney adanim tachathakeresh ha'echad lishtey yedotav. 
26:20 
For the second side of the tabernacle to the north, there shall [likewise] be 20 beams
Uletsela haMishkan hashenit lif'at tsafon esrim karesh. 

Commentary:
silver bases The outer dimensions of each base were one cubit high, one cubit thick, and 3/4 wide, one half the width of a beam. It is simple to calculate that the walls of the bases could have been no more than around 1/3 inch (0.9 cm.) thick. [Each base weighed one talent (Exodus 38:27), which is 150 pounds or 68.4 kg (see note on Exodus 25:39). Since silver has a specific gravity of 10.5, each base had a volume of 6514 cc. The circumference of each base was 3 1/2 cubits or 160 cm. and its height was one cubit or 45.72 cm. By simple division, the width of a wall comes out to be 0.9 cm. thick.]. According to the opinion that the walls of the bases were 1/4 cubit thick (Rashi on Exodus 26:17), we must say that the bases were hollow. (If they were solid, each base would weigh 627 kg. or over 9 talents, in contradiction to an explicit verse stating that each one weighed only one talent).

